Conversion of units

Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.

Techniques

See also: Dimensional analysis

Process overview

The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards. Engineering judgment may include such factors as:

• The precision and accuracy of measurement and the associated uncertainty of measurement.
• The statistical confidence interval or tolerance interval of the initial measurement.
• The number of significant figures of the measurement.
• The intended use of the measurement including the engineering tolerances.
• Historical definitions of the units and their derivatives used in old measurements; e.g., international foot vs. US survey foot.

Some conversions from one system of units to another need to be exact, without increasing or decreasing the precision of the first measurement. This is sometimes called soft conversion. It does not involve changing the physical configuration of the item being measured.

By contrast, a hard conversion or an adaptive conversion may not be exactly equivalent. It changes the measurement to convenient and workable numbers and units in the new system. It sometimes involves a slightly different configuration, or size substitution, of the item. Nominal values are sometimes allowed and used.

Conversion factors

A conversion factor is used to change the units of a measured quantity without changing its value. The unity bracket method of unit conversion consists of a fraction in which the denominator is equal to the numerator, but they are in different units. Because of the identity property of multiplication, the value of a number will not change as long as it is multiplied by one. Also, if the numerator and denominator of a fraction are equal to each other, then the fraction is equal to one. So as long as the numerator and denominator of the fraction are equivalent, they will not affect the value of the measured quantity.

Software tools

There are many conversion tools. They are found in the function libraries of applications such as spreadsheets databases, in calculators, and in macro packages and plugins for many other applications such as the mathematical, scientific and technical applications.

There are many standalone applications that offer the thousands of the various units with conversions. For example, the free software movement offers a command line utility GNU units for Linux and Windows.

Tables of conversion factors

This article gives lists of conversion factors for each of a number of physical quantities, which are listed in the index. For each physical quantity, a number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit. Conversion between units in the metric system can be discerned by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10⁻⁶ metre). Within each table, the units are listed alphabetically, and the SI units (base or derived) are highlighted.

Legend

Symbol	Definition
≡	exactly equal
≈	approximately equal to
digits	indicates that digits repeat infinitely (e.g. 8.294369 corresponds to 8.294369369369369…)
(H)	of chiefly historical interest

Length

Length

Name of unit	Symbol	Definition	Relation to SI units
ångström	Å	≡ 1×10−10 m	≡ 0.1 nm
astronomical unit	AU	≡ 149597870700 m ≈ Distance from Earth to Sun	≡ 149597870700 m
barleycorn (H)		= 1⁄3 in (see note above about rounding)	≈ 8.46×10−3 m
bohr, atomic unit of length	a0	= Bohr radius of hydrogen	≈ 5.2917721092(17)×10−11 m
cable length (imperial)		≡ 608 ft	≈ 185.3184 m
cable length (International)		≡ 1⁄10 nmi	≡ 185.2 m
cable length (US)		≡ 720 ft	= 219.456 m
chain (Gunter's; Surveyor's)	ch	≡ 66 ft (US) ≡ 4 rods	≈ 20.11684 m
cubit (H)		≡ Distance from fingers to elbow ≈ 18 in	≈ 0.5 m
ell (H)	ell	≡ 45 in (In England usually)	= 1.143 m
fathom	ftm	≡ 6 ft	= 1.8288 m
fermi	fm	≡ 1×10−15 m	≡ 1×10−15 m
finger		≡ 7⁄8 in	= 0.022225 m
finger (cloth)		≡ 4+1⁄2 in	= 0.1143 m
foot (Benoît) (H)	ft (Ben)		≈ 0.304799735 m
foot (Cape) (H)		Legally defined as 1.033 English feet in 1859	≈ 0.314858 m
foot (Clarke's) (H)	ft (Cla)		≈ 0.3047972654 m
foot (Indian) (H)	ft Ind		≈ 0.304799514 m
foot, metric	mf	≡ √1⁄10 m	≈ 0.31622776602 m
foot, metric (long)	lmf	≡ 1⁄3 m	≈ 0.3 m
foot, metric (short)	smf	≡ 0.30 m	≡ 0.30 m
foot (International)	ft	≡ 0.3048 m ≡ 1⁄3 yd ≡ 12 inches	≡ 0.3048 m
foot (Sear's) (H)	ft (Sear)		≈ 0.30479947 m
foot (US Survey)	ft (US)	≡ 1200⁄3937 m	≈ 0.304800610 m
french; charriere	F	≡ 1⁄3 mm	= 0.3 ×10−3 m
furlong	fur	≡ 10 chains = 660 ft = 220 yd	= 201.168 m
hand		≡ 4 in	≡ 0.1016 m
inch (International)	in	≡ 2.54 cm ≡ 1⁄36 yd ≡ 1⁄12 ft	≡ 0.0254 m
league (land)	lea	≈ 1 hour walk, Currently defined in US as 3 Statute miles, but historically varied from 2 to 9 km	≈ 4828 m
light-day		≡ 24 light-hours	≡ 2.59020683712×1013 m
light-hour		≡ 60 light-minutes	≡ 1.0792528488×1012 m
light-minute		≡ 60 light-seconds	≡ 1.798754748×1010 m
light-second		≡ Distance light travels in one second in vacuum	≡ 299792458 m
light-year	ly	≡ Distance light travels in vacuum in 365.25 days	= 9.4607304725808×1015 m
line	ln	≡ 1⁄12 in	= 0.002116 m
link (Gunter's; Surveyor's)	lnk	≡ 1⁄100 ch ≡ 0.66 ft (US) ≡ 7.92 in	≈ 0.2011684 m
link (Ramsden's; Engineer's)	lnk	≡ 1 ft	= 0.3048 m
metre (SI base unit) (meter)	m	≡ Distance light travels in 1⁄299792458 of a second in vacuum. ≈ 1⁄10000000 of the distance from equator to pole.	≡ 1 m
mickey		≡ 1⁄200 in	= 1.27×10−4 m
micrometre (old: micron)	µ		≡ 1×10−6 m
mil; thou	mil	≡ 1×10−3 in	≡ 2.54×10−5 m
mil (Sweden and Norway)	mil	≡ 10 km	= 10000 m
mile (geographical) (H)		≡ 6082 ft	= 1853.7936 m
mile (international)	mi	≡ 80 chains ≡ 5280 ft ≡ 1760 yd	≡ 1609.344 m
mile (tactical or data)		≡ 6000 ft	≡ 1828.8 m
mile (telegraph) (H)	mi	≡ 6087 ft	= 1855.3176 m
mile (US Survey)	mi	≡ 5280 US Survey feet ≡ (5280 × 1200⁄3937) m	≈ 1609.347219 m
nail (cloth)		≡ 2+1⁄4 in	= 0.05715 m
nanometre	nm	≡ 1×10−9 m	≡ 1×10−9 m
nautical league	NL; nl	≡ 3 nmi	= 5556 m
nautical mile (Admiralty)	NM (Adm); nmi (Adm)	= 6080 ft	= 1853.184 m
nautical mile (international)	NM; nmi	≡ 1852 m	≡ 1852 m
nautical mile (US pre 1954)		≡ 1853.248 m	≡ 1853.248 m
pace		≡ 2.5 ft	= 0.762 m
palm		≡ 3 in	= 0.0762 m
parsec	pc	Distant point with a parallax shift of one arc second from a base of one astronomical unit. ≡ ⁠648000/π⁠ AU	≈ 30856775814913700 m
pica		≡ 12 points	Dependent on point measures.
point (American, English)	pt	≡ 1⁄72.272 in	≈ 0.000351450 m
point (Didot; European)	pt	≡ 1⁄12 × 1⁄72 of pied du roi; After 1878: ≡ 5⁄133 cm	≈ 0.00037597 m; After 1878: ≈ 0.00037593985 m
point (PostScript)	pt	≡ 1⁄72 in	= 0.0003527 m
point (TeX)	pt	≡ 1⁄72.27 in	= 0.0003514598 m
quarter		≡ 1⁄4 yd	= 0.2286 m
rod; pole; perch (H)	rd	≡ 16+1⁄2 ft	= 5.0292 m
rope (H)	rope	≡ 20 ft	= 6.096 m
shaku (Japan)		≡ 10/33 m	≈ 0.303 0303 m
smoot		≡ Height of Oliver R. Smoot. ≡ 5 ft 7 in	≡ 1.7018 m
span (H)		≡ 9 in	= 0.2286 m
spat			≡ 1×1012 m
stick (H)		≡ 2 in	= 0.0508 m
picometre (old: bicron, stigma)	pm		≡ 1×10−12 m
twip	twp	≡ 1⁄1440 in	= 1.7638×10−5 m
x unit; siegbahn	xu		≈ 1.0021×10−13 m
yard (International)	yd	≡ 0.9144 m ≡ 3 ft ≡ 36 in	≡ 0.9144 m

Area

Area

Name of unit	Symbol	Definition	Relation to SI units
acre (international)	ac	≡ 1 ch × 10 ch = 4840 sq yd	≡ 4046.8564224 m2
acre (US survey)	ac	≡ 10 sq ch = 4840 sq yd, also 43560 sq ft	≈ 4046.873 m2
are	a	≡ 100 m2	= 100 m2
barn	b	≡ 10−28 m2	= 10−28 m2
barony		≡ 4000 ac	≈ 1.618742×107 m2
board	bd	≡ 1 in × 1 ft	= 7.74192×10−3 m2
boiler horsepower equivalent direct radiation	bhp EDR	≡ 1 ft2 × 1 bhp / (240 BTUIT/h)	≈ 12.958174 m2
circular inch	circ in	≡ π⁄4 sq in	≈ 5.067075×10−4 m2
circular mil; circular thou	circ mil	≡ π⁄4 mil2	≈ 5.067075×10−10 m2
cord		≡ 192 bd	= 1.48644864 m2
cuerda (PR Survey)	cda	≡ 1 cda x 1 cda = 0.971222 acre	≡ 3930.395625 m2
dunam		≡ 1000 m2	= 1000 m2
guntha (India)		≡ 121 sq yd	≈ 101.17 m2
hectare	ha	≡ 10000 m2	≡ 10000 m2
hide		≈ 120 ac (variable)	≈ 5×105 m2
rood	ro	≡ 1⁄4 ac	= 1011.7141056 m2
ping		≡ 20⁄11 m × 20⁄11 m	≈ 3.306 m2
section		≡ 1 mi × 1 mi	= 2.589988110336×106 m2
shed		≡ 10−52 m2	= 10−52 m2
square (roofing)		≡ 10 ft × 10 ft	= 9.290304 m2
square chain (international)	sq ch	≡ 66 ft × 66 ft = 1⁄10 ac	≡ 404.68564224 m2
square chain (US Survey)	sq ch	≡ 66 ft (US) × 66 ft (US) = 1⁄10 US survey acre	≈ 404.6873 m2
square foot	sq ft	≡ 1 ft × 1 ft	≡ 9.290304×10−2 m2
square foot (US Survey)	sq ft	≡ 1 ft (US) × 1 ft (US)	≈ 9.2903411613275×10−2 m2
square inch	sq in	≡ 1 in × 1 in	≡ 6.4516×10−4 m2
square kilometre	km2	≡ 1 km × 1 km	= 106 m2
square link (Gunter's)(International)	sq lnk	≡ 1 lnk × 1 lnk ≡ 0.66 ft × 0.66 ft	= 4.0468564224×10−2 m2
square link (Gunter's)(US Survey)	sq lnk	≡ 1 lnk × 1 lnk ≡ 0.66 ft (US) × 0.66 ft (US)	≈ 4.046872×10−2 m2
square link (Ramsden's)	sq lnk	≡ 1 lnk × 1 lnk ≡ 1 ft × 1 ft	= 0.09290304 m2
square metre (SI unit)	m2	≡ 1 m × 1 m	= 1 m2
square mil; square thou	sq mil	≡ 1 mil × 1 mil	= 6.4516×10−10 m2
square mile	sq mi	≡ 1 mi × 1 mi	= 2.589988110336×106 m2
square mile (US Survey)	sq mi	≡ 1 mi (US) × 1 mi (US)	≈ 2.58999847×106 m2
square rod/pole/perch	sq rd	≡ 1 rd × 1 rd	= 25.29285264 m2
square yard (International)	sq yd	≡ 1 yd × 1 yd	≡ 0.83612736 m2
stremma		≡ 1000 m2	= 1000 m2
township		≡ 36 sq mi (US)	≈ 9.323994×107 m2
yardland		≈ 30 ac	≈ 1.2×105 m2

Volume

Volume

Name of unit	Symbol	Definition	Relation to SI units
acre-foot	ac ft	≡ 1 ac x 1 ft = 43560 cu ft	= 1233.48183754752 m3
acre-inch		≡ 1 ac × 1 in	= 102.79015312896 m3
barrel (imperial)	bl (imp)	≡ 36 gal (imp)	= 0.16365924 m3
barrel (petroleum); archaic blue-barrel	bl; bbl	≡ 42 gal (US)	= 0.158987294928 m3
barrel (US dry)	bl (US)	≡ 105 qt (US) = 105/32 bu (US lvl)	= 0.115628198985075 m3
barrel (US fluid)	fl bl (US)	≡ 31+1⁄2 gal (US)	= 0.119240471196 m3
board-foot	fbm	≡ 144 cu in	≡ 2.359737216×10−3 m3
bucket (imperial)	bkt	≡ 4 gal (imp)	= 0.01818436 m3
bushel (imperial)	bu (imp)	≡ 8 gal (imp)	= 0.03636872 m3
bushel (US dry heaped)	bu (US)	≡ 1+1⁄4 bu (US lvl)	= 0.0440488377086 m3
bushel (US dry level)	bu (US lvl)	≡ 2150.42 cu in	= 0.03523907016688 m3
butt, pipe		≡ 126 gal (wine)	= 0.476961884784 m3
coomb		≡ 4 bu (imp)	= 0.14547488 m3
cord (firewood)		≡ 8 ft × 4 ft × 4 ft	= 3.624556363776 m3
cord-foot		≡ 16 cu ft	= 0.453069545472 m3
cubic fathom	cu fm	≡ 1 fm × 1 fm × 1 fm	= 6.116438863872 m3
cubic foot	cu ft	≡ 1 ft × 1 ft × 1 ft	≡ 0.028316846592 m3
cubic inch	cu in	≡ 1 in × 1 in × 1 in	≡ 16.387064×10−6 m3
cubic metre (SI unit)	m3	≡ 1 m × 1 m × 1 m	≡ 1 m3
cubic mile	cu mi	≡ 1 mi × 1 mi × 1 mi	≡ 4168181825.440579584 m3
cubic yard	cu yd	≡ 27 cu ft	≡ 0.764554857984 m3
cup (breakfast)		≡ 10 fl oz (imp)	= 284.130625×10−6 m3
cup (Canadian)	c (CA)	≡ 8 fl oz (imp)	= 227.3045×10−6 m3
cup (metric)	c	≡ 250.0×10−6 m3	= 250.0×10−6 m3
cup (US customary)	c (US)	≡ 8 US fl oz ≡ 1⁄16 gal (US)	= 236.5882365×10−6 m3
cup (US food nutrition labeling)	c (US)	≡ 240 mL	= 2.4×10−4 m3
dash (imperial)		≡ 1⁄384 gi (imp) = 1⁄2 pinch (imp)	= 369.961751302083×10−9 m3
dash (US)		≡ 1⁄96 US fl oz = 1⁄2 US pinch	= 308.057599609375×10−9 m3
dessertspoon (imperial)		≡ 1⁄12 gi (imp)	= 11.8387760416×10−6 m3
drop (imperial)	gtt	≡ 1⁄288 fl oz (imp)	= 98.6564670138×10−9 m3
drop (imperial) (alt)	gtt	≡ 1⁄1824 gi (imp)	≈ 77.886684×10−9 m3
drop (medical)		≡ 0.9964⁄12 ml	= 83.03×10−9 m3
drop (medical)		≡ 1⁄12 ml	= 83.3×10−9 m3
drop (metric)		≡ 1⁄20 mL	= 50.0×10−9 m3
drop (US)	gtt	≡ 1⁄360 US fl oz	= 82.14869322916×10−9 m3
drop (US) (alt)	gtt	≡ 1⁄456 US fl oz	≈ 64.85423149671×10−9 m3
drop (US) (alt)	gtt	≡ 1⁄576 US fl oz	≈ 51.34293326823×10−9 m3
fifth		≡ 1⁄5 US gal	= 757.0823568×10−6 m3
firkin		≡ 9 gal (imp)	= 0.04091481 m3
fluid drachm (imperial)	fl dr	≡ 1⁄8 fl oz (imp)	= 3.5516328125×10−6 m3
fluid dram (US); US fluidram	fl dr	≡ 1⁄8 US fl oz	= 3.6966911953125×10−6 m3
fluid scruple (imperial)	fl s	≡ 1⁄24 fl oz (imp)	= 1.18387760416×10−6 m3
gallon (beer)	beer gal	≡ 282 cu in	= 4.621152048×10−3 m3
gallon (imperial)	gal (imp)	≡ 4.54609 L	≡ 4.54609×10−3 m3
gallon (US dry)	gal (US)	≡ 1⁄8 bu (US lvl)	= 4.40488377086×10−3 m3
gallon (US fluid; Wine)	gal (US)	≡ 231 cu in	≡ 3.785411784×10−3 m3
gill (imperial); Noggin	gi (imp); nog	≡ 5 fl oz (imp)	= 142.0653125×10−6 m3
gill (US)	gi (US)	≡ 4 US fl oz	= 118.29411825×10−6 m3
hogshead (imperial)	hhd (imp)	≡ 2 bl (imp)	= 0.32731848 m3
hogshead (US)	hhd (US)	≡ 2 fl bl (US)	= 0.238480942392 m3
jigger (bartending)		≡ 1+1⁄2 US fl oz	≈ 44.36×10−6 m3
kilderkin		≡ 18 gal (imp)	= 0.08182962 m3
lambda	λ	≡ 1 mm3	= 1×10−9 m3
last		≡ 80 bu (imp)	= 2.9094976 m3
litre (liter)	L	≡ 1 dm3	≡ 0.001 m3
load		≡ 50 cu ft	= 1.4158423296 m3
minim (imperial)	min	≡ 1⁄480 fl oz (imp) = 1/60 fl dr (imp)	= 59.1938802083×10−9 m3
minim (US)	min	≡ 1⁄480 US fl oz = 1⁄60 US fl dr	= 61.611519921875×10−9 m3
ounce (fluid imperial)	fl oz (imp)	≡ 1⁄160 gal (imp)	≡ 28.4130625×10−6 m3
ounce (fluid US customary)	US fl oz	≡ 1⁄128 gal (US)	≡ 29.5735295625×10−6 m3
ounce (fluid US food nutrition labeling)	US fl oz	≡ 30 mL	≡ 3×10−5 m3
peck (imperial)	pk	≡ 2 gal (imp)	= 9.09218×10−3 m3
peck (US dry)	pk	≡ 1⁄4 US lvl bu	= 8.80976754172×10−3 m3
perch	per	≡ 16+1⁄2 ft × 1+1⁄2 ft × 1 ft	= 0.700841953152 m3
pinch (imperial)		≡ 1⁄192 gi (imp) = 1/16 tsp (imp)	= 739.92350260416×10−9 m3
pinch (US)		≡ 1⁄48 US fl oz = 1/16 US tsp	= 616.11519921875×10−9 m3
pint (imperial)	pt (imp)	≡ 1⁄8 gal (imp)	= 568.26125×10−6 m3
pint (US dry)	pt (US dry)	≡ 1⁄64 bu (US lvl) ≡ 1⁄8 gal (US dry)	= 550.6104713575×10−6 m3
pint (US fluid)	pt (US fl)	≡ 1⁄8 gal (US)	= 473.176473×10−6 m3
pony		≡ 3⁄4 US fl oz	= 22.180147171875×10−6 m3
pottle; quartern		≡ 1⁄2 gal (imp) = 80 fl oz (imp)	= 2.273045×10−3 m3
quart (imperial)	qt (imp)	≡ 1⁄4 gal (imp)	= 1.1365225×10−3 m3
quart (US dry)	qt (US)	≡ 1⁄32 bu (US lvl) = 1⁄4 gal (US dry)	= 1.101220942715×10−3 m3
quart (US fluid)	qt (US)	≡ 1⁄4 gal (US fl)	= 946.352946×10−6 m3
quarter; pail		≡ 8 bu (imp)	= 0.29094976 m3
register ton		≡ 100 cu ft	= 2.8316846592 m3
sack (imperial); bag		≡ 3 bu (imp)	= 0.10910616 m3
sack (US)		≡ 3 bu (US lvl)	= 0.10571721050064 m3
seam		≡ 8 bu (US lvl)	= 0.28191256133504 m3
shot (US)		usually 1.5 US fl oz	≈ 44×10−6 m3
strike (imperial)		≡ 2 bu (imp)	= 0.07273744 m3
strike (US)		≡ 2 bu (US lvl)	= 0.07047814033376 m3
tablespoon (Australian metric)			≡ 20.0×10−6 m3
tablespoon (Canadian)	tbsp	≡ 1⁄2 fl oz (imp)	= 14.20653125×10−6 m3
tablespoon (imperial)	tbsp	≡ 5⁄8 fl oz (imp)	= 17.7581640625×10−6 m3
tablespoon (metric)			≡ 15.0×10−6 m3
tablespoon (US customary)	tbsp	≡ 1⁄2 US fl oz	= 14.78676478125×10−6 m3
tablespoon (US food nutrition labeling)	tbsp	≡ 15 mL	= 1.5×10−5 m3
teaspoon (Canadian)	tsp	≡ 1⁄6 fl oz (imp)	= 4.735510416×10−6 m3
teaspoon (imperial)	tsp	≡ 1⁄24 gi (imp)	= 5.91938802083×10−6 m3
teaspoon (metric)		≡ 5.0×10−6 m3	= 5.0×10−6 m3
teaspoon (US customary)	tsp	≡ 1⁄6 US fl oz	= 4.92892159375×10−6 m3
teaspoon (US food nutrition labeling)	tsp	≡ 5 mL	= 5×10−6 m3
timber foot		≡ 1 cu ft	= 0.028316846592 m3
ton (displacement)		≡ 35 cu ft	= 0.99108963072 m3
ton (freight)		≡ 40 cu ft	= 1.13267386368 m3
ton (water)		≡ 28 bu (imp)	= 1.01832416 m3
tun		≡ 252 gal (wine)	= 0.953923769568 m3
wey (US)		≡ 40 bu (US lvl)	= 1.4095628066752 m3

Plane angle

Plane angle

Name of unit	Symbol	Definition	Relation to SI units
angular mil	µ	≡ 2π⁄6400 rad	≈ 0.981748×10−3 rad
arcminute; MOA	'	≡ 1°⁄60	≈ 0.290888×10−3 rad
arcsecond	"	≡ 1°⁄3600	≈ 4.848137×10−6 rad
centesimal minute of arc	'	≡ 1⁄100 grad	≈ 0.157080×10−3 rad
centesimal second of arc	"	≡ 1⁄10000 grad	≈ 1.570796×10−6 rad
degree (of arc)	°	≡ 1⁄360 of a revolution ≡ π⁄180 rad	≈ 17.453293×10−3 rad
grad; gradian; gon	grad	≡ 1⁄400 of a revolution ≡ π⁄200 rad ≡ 0.9°	≈ 15.707963×10−3 rad
octant		≡ 45°	≈ 0.785398 rad
quadrant		≡ 90°	≈ 1.570796 rad
radian (SI unit)	rad	The angle subtended at the center of a circle by an arc whose length is equal to the circle's radius. One full revolution encompasses 2π radians.	= 1 rad
sextant		≡ 60°	≈ 1.047198 rad
sign		≡ 30°	≈ 0.523599 rad

Solid angle

Solid angle

Name of unit	Symbol	Definition	Relation to SI units
square degree	deg2; sq.deg.; (°)2	≡ (π⁄180)2 sr	≈ 0.30462×10−3 sr
steradian (SI unit)	sr	The solid angle subtended at the center of a sphere of radius r by a portion of the surface of the sphere having an area r2. A sphere encompasses 4π sr.	= 1 sr

Mass

Notes:

• See Weight for detail of mass/weight distinction and conversion.
• Avoirdupois is a system of mass based on a pound of 16 ounces, while Troy weight is the system of mass where 12 troy ounces equals one troy pound.
• In this table, the unit gee is used to denote standard gravity in order to avoid confusion with the "g" symbol for grams.
• In physics, the pound of mass is sometimes written lbm to distinguish it from the pound-force (lbf). It should not be read as the mongrel unit "pound metre".

Mass

Name of unit	Symbol	Definition	Relation to SI units
atomic mass unit, unified	u; AMU		≈ 1.660538921(73)×10−27 kg
atomic unit of mass, electron rest mass	me		≈ 9.10938291(40)×10−31 kg
bag (coffee)		≡ 60 kg	= 60 kg
bag (Portland cement)		≡ 94 lb av	= 42.63768278 kg
barge		≡ 22+1⁄2 short ton	= 20411.65665 kg
carat	kt	≡ 3+1⁄6 gr	= 205.1965483 mg
carat (metric)	ct	≡ 200 mg	= 200 mg
clove		≡ 8 lb av	= 3.62873896 kg
crith			≈ 89.9349 mg
dalton	Da		≈ 1.660538921(73)×10−27 kg
dram (apothecary; troy)	dr t	≡ 60 gr	= 3.8879346 g
dram (avoirdupois)	dr av	≡ 27+11⁄32 gr	= 1.7718451953125 g
electronvolt	eV	≡ 1 eV (energy unit) / c2	= 1.78266184(45)×10−36 kg
gamma	γ	≡ 1 μg	= 1 μg
grain	gr	≡ 1⁄7000 lb av	≡ 64.79891 mg
grave	gv.	grave was the original name of the kilogram	≡ 1 kg
hundredweight (long)	long cwt or cwt	≡ 112 lb av	= 50.80234544 kg
hundredweight (short); cental	sh cwt	≡ 100 lb av	= 45.359237 kg
kilogram (kilogramme)	kg	≡ mass of the prototype near Paris (≈ mass of 1 L of water)	≡ 1 kg (SI base unit)
kip	kip	≡ 1000 lb av	= 453.59237 kg
mark		≡ 8 oz t	= 248.8278144 g
mite		≡ 1⁄20 gr	= 3.2399455 mg
mite (metric)		≡ 1⁄20 g	= 50 mg
ounce (apothecary; troy)	oz t	≡ 1⁄12 lb t	= 31.1034768 g
ounce (avoirdupois)	oz av	≡ 1⁄16 lb	= 28.349523125 g
ounce (US food nutrition labelling)	oz	≡ 28 g	= 28 g
pennyweight	dwt; pwt	≡ 1⁄20 oz t	= 1.55517384 g
point		≡ 1⁄100 ct	= 2 mg
pound (avoirdupois)	lb av	≡ 0.45359237 kg = 7000 grains	≡ 0.45359237 kg
pound (metric)		≡ 500 g	= 500 g
pound (troy)	lb t	≡ 5760 grains	= 0.3732417216 kg
quarter (imperial)		≡ 1⁄4 long cwt = 2 st = 28 lb av	= 12.70058636 kg
quarter (informal)		≡ 1⁄4 short ton	= 226.796185 kg
quarter, long (informal)		≡ 1⁄4 long ton	= 254.0117272 kg
quintal (metric)	q	≡ 100 kg	= 100 kg
scruple (apothecary)	s ap	≡ 20 gr	= 1.2959782 g
sheet		≡ 1⁄700 lb av	= 647.9891 mg
slug; geepound; hyl	slug	≡ 1 ɡ0 × 1 lb av × 1 s2/ft	≈ 14.593903 kg
stone	st	≡ 14 lb av	= 6.35029318 kg
ton, assay (long)	AT	≡ 1 mg × 1 long ton ÷ 1 oz t	= 32.6 g
ton, assay (short)	AT	≡ 1 mg × 1 short ton ÷ 1 oz t	= 29.16 g
ton, long	long tn or ton	≡ 2240 lb	= 1016.0469088 kg
ton, short	sh tn	≡ 2000 lb	= 907.18474 kg
tonne (mts unit)	t	≡ 1000 kg	= 1000 kg
wey		≡ 252 lb = 18 st	= 114.30527724 kg (variants exist)
Zentner	Ztr.	Definitions vary.

Density

Density

Name of unit	Symbol	Definition	Relation to SI units
gram per millilitre	g/mL	≡ g/mL	= 1000 kg/m3
kilogram per cubic metre (SI unit)	kg/m3	≡ kg/m3	= 1 kg/m3
kilogram per litre	kg/L	≡ kg/L	= 1000 kg/m3
ounce (avoirdupois) per cubic foot	oz/ft3	≡ oz/ft3	≈ 1.001153961 kg/m3
ounce (avoirdupois) per cubic inch	oz/in3	≡ oz/in3	≈ 1.729994044×103 kg/m3
ounce (avoirdupois) per gallon (imperial)	oz/gal	≡ oz/gal	≈ 6.236023291 kg/m3
ounce (avoirdupois) per gallon (US fluid)	oz/gal	≡ oz/gal	≈ 7.489151707 kg/m3
pound (avoirdupois) per cubic foot	lb/ft3	≡ lb/ft3	≈ 16.01846337 kg/m3
pound (avoirdupois) per cubic inch	lb/in3	≡ lb/in3	≈ 2.767990471×104 kg/m3
pound (avoirdupois) per gallon (imperial)	lb/gal	≡ lb/gal	≈ 99.77637266 kg/m3
pound (avoirdupois) per gallon (US fluid)	lb/gal	≡ lb/gal	≈ 119.8264273 kg/m3
slug per cubic foot	slug/ft3	≡ slug/ft3	≈ 515.3788184 kg/m3

Time

Time

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of time	au	≡ a0/(α·c)	≈ 2.418884254×10−17 s
Callippic cycle		≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d	= 2.396736 Gs or 2.3983776 Gs
century	c	≡ 100 years (100 a)	= 3.1556952 Gs
day	d	= 24 h = 1440 min	= 86.4 ks
day (sidereal)	d	≡ Time needed for the Earth to rotate once around its axis, determined from successive transits of a very distant astronomical object across an observer's meridian (International Celestial Reference Frame)	≈ 86.1641 ks
decade	dec	≡ 10 years (10 a)	= 315.569520 Ms
fortnight	fn	≡ 2 wk	= 1.2096 Ms
helek		≡ 1⁄1080 h	= 3.3 s
Hipparchic cycle		≡ 4 Callippic cycles - 1 d	= 9.593424 Gs
hour	h	≡ 60 min	= 3.6 ks
jiffy	j	≡ 1⁄60 s	= 16.6 ms
jiffy (alternative)	ja	≡ 1⁄100 s	= 10 ms
ke (quarter of an hour)		≡ 1⁄4 h = 1⁄96 d = 15 min	= 900 s
ke (traditional)		≡ 1⁄100 d = 14.4 min	= 864 s
lustre; lustrum		≡ 5 a of 365 d	= 157.68 Ms
Metonic cycle; enneadecaeteris		≡ 110 mo (hollow) + 125 mo (full) = 6940 d ≈ 19 a	= 599.616 Ms
millennium		≡ 1000 years (1000 a)	= 31.556952 Gs
milliday	md	≡ 1⁄1000 d	= 86.4 s
minute	min	≡ 60 s, due to leap seconds sometimes 59 s or 61 s,	= 60 s
moment		≡ 90 s	= 90 s
month (full)	mo	≡ 30 d	= 2.592×106 s
month (Greg. av.)	mo	= 30.436875 d	≈ 2.6297 Ms
month (hollow)	mo	≡ 29 d	= 2.5056 Ms
month (synodic)	mo	Cycle time of moon phases ≈ 29.530589 d (average)	≈ 2.551 Ms
octaeteris		= 48 mo (full) + 48 mo (hollow) + 3 mo (full) = 8 a of 365.25 d = 2922 d	= 252.4608 Ms
Planck time		≡ (Gℏ⁄c5)1⁄2	≈ 1.351211868×10−43 s
second	s	time of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom at 0 K (but other seconds are sometimes used in astronomy). Also that time it takes for light to travel a distance of 299792458 metres.	(SI base unit)
shake		≡ 10−8 s	= 10 ns
sigma		≡ 10−6 s	= 1 μs
Sothic cycle		≡ 1461 a of 365 d	= 460.74096 Ts
svedberg	S	≡ 10−13 s	= 100 fs
week	wk	≡ 7 d = 168 h = 10080 min	= 604.8 ks
year (common)	a, y, or yr	365 d	= 31.536 Ms
year (Gregorian)	a, y, or yr	= 365.2425 d average, calculated from common years (365 d) plus leap years (366 d) on most years divisible by 4. See leap year for details.	= 31.556952 Ms
year (Julian)	a, y, or yr	= 365.25 d average, calculated from common years (365 d) plus one leap year (366 d) every four years	= 31.5576 Ms
year (leap)	a, y, or yr	366 d	= 31.6224 Ms
year (mean tropical)	a, y, or yr	conceptually, the length of time it takes for the Sun to return to the same position in the cycle of seasons, approximately 365.24219 d, each day being 86400 SI seconds	≈ 31.556925 Ms
year (sidereal)	a, y, or yr	≡ time taken for Sun to return to the same position with respect to the stars of the celestial sphere, approximately 365.256363 d	≈ 31.5581497632 Ms
Notes:

Frequency

Frequency

Name of unit	Symbol	Definition	Relation to SI units
hertz (SI unit)	Hz	≡ Number of cycles per second	= 1 Hz = 1/s
revolutions per minute	rpm	≡ One unit rpm equals one rotation completed around a fixed axis in one minute of time.	≈ 0.104719755 rad/s

Speed or velocity

Speed

Name of unit	Symbol	Definition	Relation to SI units
foot per hour	fph	≡ 1 ft/h	= 8.46×10−5 m/s
foot per minute	fpm	≡ 1 ft/min	= 5.08×10−3 m/s
foot per second	fps	≡ 1 ft/s	= 3.048×10−1 m/s
furlong per fortnight		≡ furlong/fortnight	≈ 1.663095×10−4 m/s
inch per hour	iph	≡ 1 in/h	= 7.05×10−6 m/s
inch per minute	ipm	≡ 1 in/min	= 4.23×10−4 m/s
inch per second	ips	≡ 1 in/s	= 2.54×10−2 m/s
kilometre per hour	km/h	≡ 1 km/h	= 2.7×10−1 m/s
knot	kn	≡ 1 nmi/h = 1.852 km/h	= 0.514 m/s
knot (Admiralty)	kn	≡ 1 NM (Adm)/h = 1.853184 km/h	= 0.514773 m/s
mach number	M	Ratio of the speed to the speed of sound in the medium (unitless).	≈ 340 to 295 m/s
metre per second (SI unit)	m/s	≡ 1 m/s	= 1 m/s
mile per hour	mph	≡ 1 mi/h	= 0.44704 m/s
mile per minute	mpm	≡ 1 mi/min	= 26.8224 m/s
mile per second	mps	≡ 1 mi/s	= 1609.344 m/s
speed of light in vacuum	c	≡ 299792458 m/s	= 299792458 m/s
speed of sound in air	s	1225 to 1062 km/h (761–660 mph or 661–574 kn)	≈ 340 to 295 m/s
Note

A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.

Flow (volume)

Flow

Name of unit	Symbol	Definition	Relation to SI units
cubic foot per minute	CFM	≡ 1 ft3/min	= 4.719474432×10−4 m3/s
cubic foot per second	ft3/s	≡ 1 ft3/s	= 0.028316846592 m3/s
cubic inch per minute	in3/min	≡ 1 in3/min	= 2.7311773×10−7 m3/s
cubic inch per second	in3/s	≡ 1 in3/s	= 1.6387064×10−5 m3/s
cubic metre per second (SI unit)	m3/s	≡ 1 m3/s	= 1 m3/s
gallon (US fluid) per day	GPD	≡ 1 gal/d	= 4.381263638×10−8 m3/s
gallon (US fluid) per hour	GPH	≡ 1 gal/h	= 1.051503273×10−6 m3/s
gallon (US fluid) per minute	GPM	≡ 1 gal/min	= 6.30901964×10−5 m3/s
litre per minute	LPM	≡ 1 L/min	= 1.6×10−5 m3/s

Acceleration

Acceleration

Name of unit	Symbol	Definition	Relation to SI units
foot per hour per second	fph/s	≡ 1 ft/(h·s)	= 8.46×10−5 m/s2
foot per minute per second	fpm/s	≡ 1 ft/(min·s)	= 5.08×10−3 m/s2
foot per second squared	fps2	≡ 1 ft/s2	= 3.048×10−1 m/s2
gal; galileo	Gal	≡ 1 cm/s2	= 10−2 m/s2
inch per minute per second	ipm/s	≡ 1 in/(min·s)	= 4.23×10−4 m/s2
inch per second squared	ips2	≡ 1 in/s2	= 2.54×10−2 m/s2
knot per second	kn/s	≡ 1 kn/s	≈ 5.14×10−1 m/s2
metre per second squared (SI unit)	m/s2	≡ 1 m/s2	= 1 m/s2
mile per hour per second	mph/s	≡ 1 mi/(h·s)	= 4.4704×10−1 m/s2
mile per minute per second	mpm/s	≡ 1 mi/(min·s)	= 26.8224 m/s2
mile per second squared	mps2	≡ 1 mi/s2	= 1.609344×103 m/s2
standard gravity	ɡ0	≡ 9.80665 m/s2	= 9.80665 m/s2

Force

Force

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of force		≡ me·α2·c2⁄a0	≈ 8.23872206×10−8 N
dyne (cgs unit)	dyn	≡ g·cm/s2	= 10−5 N
kilogram-force; kilopond; grave-force	kgf; kp; Gf	≡ ɡ0 × 1 kg	= 9.80665 N
kip; kip-force	kip; kipf; klbf	≡ ɡ0 × 1000 lb	= 4.4482216152605×103 N
milligrave-force, gravet-force	mGf; gf	≡ ɡ0 × 1 g	= 9.80665 mN
long ton-force	tnf	≡ ɡ0 × 1 short ton	= 9.96401641818352×103 N
newton (SI unit)	N	A force capable of giving a mass of one kilogram an acceleration of one metre per second per second.	= 1 N = 1 kg·m/s2
ounce-force	ozf	≡ ɡ0 × 1 oz	= 0.27801385095378125 N
pound-force	lbf	≡ ɡ0 × 1 lb	= 4.4482216152605 N
poundal	pdl	≡ 1 lb·ft/s2	= 0.138254954376 N
short ton-force	tnf	≡ ɡ0 × 1 short ton	= 8.896443230521×103 N
sthene (mts unit)	sn	≡ 1 t·m/s2	= 103 N

See also: Conversion between weight (force) and mass

Pressure or mechanical stress

Pressure

Name of unit	Symbol	Definition	Relation to SI units
atmosphere (standard)	atm		≡ 101325 Pa
atmosphere (technical)	at	≡ 1 kgf/cm2	= 9.80665×104 Pa
bar	bar		≡ 105 Pa
barye (cgs unit)		≡ 1 dyn/cm2	= 0.1 Pa
centimetre of mercury	cmHg	≡ 13595.1 kg/m3 × 1 cm × ɡ0	≈ 1.33322×103 Pa
centimetre of water (4 °C)	cmH2O	≈ 999.972 kg/m3 × 1 cm × ɡ0	≈ 98.0638 Pa
foot of mercury (conventional)	ftHg	≡ 13595.1 kg/m3 × 1 ft × ɡ0	≈ 4.063666×104 Pa
foot of water (39.2 °F)	ftH2O	≈ 999.972 kg/m3 × 1 ft × ɡ0	≈ 2.98898×103 Pa
inch of mercury (conventional)	inHg	≡ 13595.1 kg/m3 × 1 in × ɡ0	≈ 3.386389×103 Pa
inch of water (39.2 °F)	inH2O	≈ 999.972 kg/m3 × 1 in × ɡ0	≈ 249.082 Pa
kilogram-force per square millimetre	kgf/mm2	≡ 1 kgf/mm2	= 9.80665×106 Pa
kip per square inch	ksi	≡ 1 kipf/sq in	≈ 6.894757×106 Pa
long ton per square foot		≡ 1 long ton × ɡ0 / 1 sq ft	≈ 1.0725178011595×105 Pa
micrometre of mercury	$\mu$mHg	≡ 13595.1 kg/m3 × 1 $\mu$m × ɡ0 ≈ 0.001 torr	≈ 0.1333224 Pa
millimetre of mercury	mmHg	≡ 13595.1 kg/m3 × 1 mm × ɡ0 ≈ 1 torr	≈ 133.3224 Pa
millimetre of water (3.98 °C)	mmH2O	≈ 999.972 kg/m3 × 1 mm × ɡ0 = 0.999972 kgf/m2	= 9.80638 Pa
pascal (SI unit)	Pa	≡ N/m2 = kg/(m·s2)	= 1 Pa
pièze (mts unit)	pz	≡ 1000 kg/m·s2	= 103 Pa = 1 kPa
pound per square foot	psf	≡ 1 lbf/ft2	≈ 47.88026 Pa
pound per square inch	psi	≡ 1 lbf/in2	≈ 6.894757×103 Pa
poundal per square foot	pdl/sq ft	≡ 1 pdl/sq ft	≈ 1.488164 Pa
short ton per square foot		≡ 1 short ton × ɡ0 / 1 sq ft	≈ 9.5760518×104 Pa
torr	torr	≡ 101325⁄760 Pa	≈ 133.3224 Pa

Torque or moment of force

Torque

Name of unit	Symbol	Definition	Relation to SI units
foot-pound force	ft·lbf	≡ ɡ0 × 1 lb × 1 ft	= 1.3558179483314004 N⋅m
foot-poundal	ft·pdl	≡ 1 lb·ft2/s2	= 4.21401100938048×10−2 N⋅m
inch-pound force	in·lbf	≡ ɡ0 × 1 lb × 1 in	= 0.1129848290276167 N⋅m
metre kilogram-force	m·kgf	≡ ɡ0 × N × m	= 9.80665 N⋅m
Newton metre (SI unit)	N·m	≡ N × m = kg·m2/s2	= 1 N⋅m

Energy

Energy

Name of unit	Symbol	Definition	Relation to SI units
barrel of oil equivalent	boe	≈ 5.8×106 BTU59 °F	≈ 6.12×109 J
British thermal unit (ISO)	BTUISO	≡ 1.0545×103 J	= 1.0545×103 J
British thermal unit (International Table)	BTUIT		= 1.05505585262×103 J
British thermal unit (mean)	BTUmean		≈ 1.05587×103 J
British thermal unit (thermochemical)	BTUth		≈ 1.054350×103 J
British thermal unit (39 °F)	BTU39 °F		≈ 1.05967×103 J
British thermal unit (59 °F)	BTU59 °F	≡ 1.054804×103 J	= 1.054804×103 J
British thermal unit (60 °F)	BTU60 °F		≈ 1.05468×103 J
British thermal unit (63 °F)	BTU63 °F		≈ 1.0546×103 J
calorie (International Table)	calIT	≡ 4.1868 J	= 4.1868 J
calorie (mean)	calmean	1⁄100 of the energy required to warm one gram of air-free water from 0 °C to 100 °C @ 1 atm	≈ 4.19002 J
calorie (thermochemical)	calth	≡ 4.184 J	= 4.184 J
Calorie (US; FDA)	Cal	≡ 1 kcal = 1000 cal	= 4184 J
calorie (3.98 °C)	cal3.98 °C		≈ 4.2045 J
calorie (15 °C)	cal15 °C	≡ 4.1855 J	= 4.1855 J
calorie (20 °C)	cal20 °C		≈ 4.1819 J
Celsius heat unit (International Table)	CHUIT	≡ 1 BTUIT × 1 K/°R	= 1.899100534716×103 J
cubic centimetre of atmosphere; standard cubic centimetre	cc atm; scc	≡ 1 atm × 1 cm3	= 0.101325 J
cubic foot of atmosphere; standard cubic foot	cu ft atm; scf	≡ 1 atm × 1 ft3	= 2.8692044809344×103 J
cubic foot of natural gas		≡ 1000 BTUIT	= 1.05505585262×106 J
cubic yard of atmosphere; standard cubic yard	cu yd atm; scy	≡ 1 atm × 1 yd3	= 77.4685209852288×103 J
electronvolt	eV	≡ e × 1 V	≈ 1.602176565(35)×10−19 J
erg (cgs unit)	erg	≡ 1 g·cm2/s2	= 10−7 J
foot-pound force	ft lbf	≡ ɡ0 × 1 lb × 1 ft	= 1.3558179483314004 J
foot-poundal	ft pdl	≡ 1 lb·ft2/s2	= 4.21401100938048×10−2 J
gallon-atmosphere (imperial)	imp gal atm	≡ 1 atm × 1 gal (imp)	= 460.63256925 J
gallon-atmosphere (US)	US gal atm	≡ 1 atm × 1 gal (US)	= 383.5568490138 J
hartree, atomic unit of energy	Eh	≡ me·α2·c2 (= 2 Ry)	≈ 4.359744×10−18 J
horsepower-hour	hp·h	≡ 1 hp × 1 h	= 2.684519537696172792×106 J
inch-pound force	in lbf	≡ ɡ0 × 1 lb × 1 in	= 0.1129848290276167 J
joule (SI unit)	J	The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force.	= 1 J = 1 m·N = 1 kg·m2/s2 = 1 C·V = 1 W·s
kilocalorie; large calorie	kcal; Cal	≡ 1000 calIT	= 4.1868×103 J
kilowatt-hour; Board of Trade Unit	kW·h; B.O.T.U.	≡ 1 kW × 1 h	= 3.6×106 J
litre-atmosphere	l atm; sl	≡ 1 atm × 1 L	= 101.325 J
quad		≡ 1015 BTUIT	= 1.05505585262×1018 J
rydberg	Ry	≡ R∞·ℎ·c	≈ 2.179872×10−18 J
therm (E.C.)		≡ 100000 BTUIT	= 105.505585262×106 J
therm (US)		≡ 100000 BTU59 °F	= 105.4804×106 J
thermie	th	≡ 1 McalIT	= 4.1868×106 J
ton of coal equivalent	TCE	≡ 7 Gcalth	= 29.288×109 J
tonne of oil equivalent	toe	≡ 10 GcalIT	= 41.868×109 J
ton of TNT	tTNT	≡ 1 Gcalth	= 4.184×109 J

Power or heat flow rate

Power

Name of unit	Symbol	Definition	Relation to SI units
atmosphere-cubic centimetre per minute	atm ccm	≡ 1 atm × 1 cm3/min	= 1.68875×10−3 W
atmosphere-cubic centimetre per second	atm ccs	≡ 1 atm × 1 cm3/s	= 0.101325 W
atmosphere-cubic foot per hour	atm cfh	≡ 1 atm × 1 cu ft/h	= 0.79700124704 W
atmosphere-cubic foot per minute	atm cfm	≡ 1 atm × 1 cu ft/min	= 47.82007468224 W
atmosphere-cubic foot per second	atm cfs	≡ 1 atm × 1 cu ft/s	= 2.8692044809344×103 W
BTU (International Table) per hour	BTUIT/h	≡ 1 BTUIT/h	≈ 0.293071 W
BTU (International Table) per minute	BTUIT/min	≡ 1 BTUIT/min	≈ 17.584264 W
BTU (International Table) per second	BTUIT/s	≡ 1 BTUIT/s	= 1.05505585262×103 W
calorie (International Table) per second	calIT/s	≡ 1 calIT/s	= 4.1868 W
erg per second	erg/s	≡ 1 erg/s	= 10−7 W
foot-pound-force per hour	ft·lbf/h	≡ 1 ft lbf/h	≈ 3.766161×10−4 W
foot-pound-force per minute	ft·lbf/min	≡ 1 ft lbf/min	= 2.259696580552334×10−2 W
foot-pound-force per second	ft·lbf/s	≡ 1 ft lbf/s	= 1.3558179483314004 W
horsepower (boiler)	hp	≈ 34.5 lb/h × 970.3 BTUIT/lb	≈ 9809.5 W
horsepower (European electrical)	hp	≡ 75 kp·m/s	= 736 W
horsepower (electrical)	hp	≡ 746 W	= 746 W
horsepower (mechanical)	hp	≡ 550 ft·lbf/s	= 745.69987158227022 W
horsepower (metric)	hp or PS	≡ 75 m·kgf/s	= 735.49875 W
litre-atmosphere per minute	L·atm/min	≡ 1 atm × 1 L/min	= 1.68875 W
litre-atmosphere per second	L·atm/s	≡ 1 atm × 1 L/s	= 101.325 W
lusec	lusec	≡ 1 L·µmHg/s	≈ 1.333×10−4 W
poncelet	p	≡ 100 m·kgf/s	= 980.665 W
square foot equivalent direct radiation	sq ft EDR	≡ 240 BTUIT/h	≈ 70.337057 W
ton of air conditioning		≡ 2000 lb of ice melted / 24 h	≈ 3504 W
ton of refrigeration (imperial)		≡ 2240 lb × iceIT / 24 h: iceIT = 144 °F × 2326 J/kg·°F	≈ 3.938875×103 W
ton of refrigeration (IT)		≡ 2000 lb × iceIT / 24 h: iceIT = 144 °F × 2326 J/kg·°F	≈ 3.516853×103 W
watt (SI unit)	W	The power which in one second of time gives rise to one joule of energy.	= 1 W = 1 J/s = 1 N·m/s = 1 kg·m2/s3

Action

Action

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of action	au	≡ ℏ ≡ ℎ⁄2π	≈ 1.05457168×10−34 J·s

Dynamic viscosity

Dynamic viscosity

Name of unit	Symbol	Definition	Relation to SI units
pascal second (SI unit)	Pa·s	≡ N·s/m2, kg/(m·s)	= 1 Pa·s
poise (cgs unit)	P	≡ 1 barye·s	= 0.1 Pa·s
pound per foot hour	lb/(ft·h)	≡ 1 lb/(ft·h)	≈ 4.133789×10−4 Pa·s
pound per foot second	lb/(ft·s)	≡ 1 lb/(ft·s)	≈ 1.488164 Pa·s
pound-force second per square foot	lbf·s/ft2	≡ 1 lbf·s/ft2	≈ 47.88026 Pa·s
pound-force second per square inch	lbf·s/in2	≡ 1 lbf·s/in2	≈ 6894.757 Pa·s

Kinematic viscosity

Kinematic viscosity

Name of unit	Symbol	Definition	Relation to SI units
square foot per second	ft2/s	≡ 1 ft2/s	= 0.09290304 m2/s
square metre per second (SI unit)	m2/s	≡ 1 m2/s	= 1 m2/s
stokes (cgs unit)	St	≡ 1 cm2/s	= 10−4 m2/s

Electric current

Electric current

Name of unit	Symbol	Definition	Relation to SI units
ampere (SI base unit)	A	≡ The constant current needed to produce a force of 2 ×10−7 newton per metre between two straight parallel conductors of infinite length and negligible circular cross-section placed one metre apart in a vacuum.	= 1 A = 1 C/s
electromagnetic unit; abampere (cgs unit)	abamp	≡ 10 A	= 10 A
esu per second; statampere (cgs unit)	esu/s	≡ 0.1 A·m/s⁄c	≈ 3.335641×10−10 A

Electric charge

Electric charge

Name of unit	Symbol	Definition	Relation to SI units
abcoulomb; electromagnetic unit (cgs unit)	abC; emu	≡ 10 C	= 10 C
atomic unit of charge	au	≡ e	≈ 1.602176462×10−19 C
coulomb	C	≡ The amount of electricity carried in one second of time by one ampere of current.	= 1 C = 1 A·s
faraday	F	≡ 1 mol × NA·e	≈ 96485.3383 C
milliampere hour	mA·h	≡ 0.001 A × 1 h	= 3.6 C
statcoulomb; franklin; electrostatic unit (cgs unit)	statC; Fr; esu	≡ 0.1 A·m⁄c	≈ 3.335641×10−10 C

Electric dipole

Electric dipole

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of electric dipole moment	ea0		≈ 8.47835281×10−30 C·m
coulomb meter	C·m		= 1 C · 1 m
debye	D	= 10−10 esu·Å	= 3.33564095×10−30 C·m

Electromotive force, electric potential difference

Voltage, electromotive force

Name of unit	Symbol	Definition	Relation to SI units
abvolt (cgs unit)	abV	≡ 10−8 V	= 10−8 V
statvolt (cgs unit)	statV	≡ c·(1 μJ/A·m)	= 299.792458 V
volt (SI unit)	V	The difference in electric potential across two points along a conducting wire carrying one ampere of constant current when the power dissipated between the points equals one watt.	= 1 V = 1 W/A = 1 kg·m2/(A·s3)

Electrical resistance

Electrical resistance

Name of unit	Symbol	Definition	Relation to SI units
ohm (SI unit)	Ω	The resistance between two points in a conductor when one volt of electric potential difference, applied to these points, produces one ampere of current in the conductor.	= 1 Ω = 1 V/A = 1 kg·m2/(A2·s3)

Capacitance

Capacitor's ability to store charge

Name of unit	Symbol	Definition	Relation to SI units
farad (SI unit)	F	The capacitance between two parallel plates that results in one volt of potential difference when charged by one coulomb of electricity.	= 1 F = 1 C/V = 1 A2·s4/(kg·m2)

Magnetic flux

magnetic flux

Name of unit	Symbol	Definition	Relation to SI units
maxwell (CGS unit)	Mx	≡ 10−8 Wb	= 10−8 Wb
weber (SI unit)	Wb	Magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.	= 1 Wb = 1 V·s = 1 kg·m2/(A·s2)

Magnetic flux density

What physicists call Magnetic field is called Magnetic flux density by electrical engineers and magnetic induction by applied mathematicians and electrical engineers.

Name of unit	Symbol	Definition	Relation to SI units
gauss (CGS unit)	G	≡ Mx/cm2 = 10−4 T	= 10−4 T
tesla (SI unit)	T	≡ Wb/m2	= 1 T = 1 Wb/m2 = 1 kg/(A·s2)

Inductance

Inductance

Name of unit	Symbol	Definition	Relation to SI units
henry (SI unit)	H	The inductance of a closed circuit that produces one volt of electromotive force when the current in the circuit varies at a uniform rate of one ampere per second.	= 1 H = 1 Wb/A = 1 kg·m2/(A·s)2

Temperature

Further information: Conversion of units of temperature

Temperature

Name of unit	Symbol	Definition	Relation to SI units
degree Celsius	°C	[°C] ≡ [K] − 273.15	[K] ≡ [°C] + 273.15
degree Delisle	°De		[K] = 373.15 − [°De] × 2⁄3
degree Fahrenheit	°F	[°F] ≡ [°C] × 9⁄5 + 32	[K] ≡ ([°F] + 459.67) × 5⁄9
degree Newton	°N		[K] = [°N] × 100⁄33 + 273.15
degree Rankine	°R;	[°R] ≡ [K] × 9⁄5	[K] ≡ [°R] × 5/9
degree Réaumur	°Ré		[K] = [°Ré] × 5⁄4 + 273.15
degree Rømer	°Rø		[K] = ([°Rø] − 7.5) × 40⁄21 + 273.15
Regulo Gas Mark	GM;	[°F] ≡ [GM] × 25 + 300	[K] ≡ [GM] × 125⁄9 + 422.038
kelvin (SI base unit)	K	≡ 1⁄273.16 of the thermodynamic temperature of the triple point of water.	≡ 1 K

Information entropy

Information entropy

Name of unit	Symbol	Definition	Relation to SI units	Relation to bits
SI unit	J/K	≡ J/K	= 1 J/K
nat; nip; nepit	nat	≡ kB	= 1.3806505(23)×10−23 J/K
bit; shannon	bit; b; Sh	≡ ln(2) × kB	= 9.569940(16)×10−24 J/K	= 1 bit
ban; hartley	ban; Hart	≡ ln(10) × kB	= 3.1790653(53)×10−23 J/K
nibble		≡ 4 bits	= 3.8279760(64)×10−23 J/K	= 22 bit
byte	B	≡ 8 bits	= 7.655952(13)×10−23 J/K	= 23 bit
kilobyte (decimal)	kB	≡ 1000 B	= 7.655952(13)×10−20 J/K	= 8000 bit
kilobyte (kibibyte)	KB; KiB	≡ 1024 B	= 7.839695(13)×10−20 J/K	= 213 bit = 8192 bit

Often, information entropy is measured in shannons, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning. Other times the bit is used as a measure of information entropy and is thus a synonym of shannon.

Luminous intensity

The candela is the preferred nomenclature for the SI unit.

Luminous intensity

Name of unit	Symbol	Definition	Relation to SI units
candela (SI base unit); candle	cd	The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.	= 1 cd
candlepower (new)	cp	≡ cd The use of candlepower as a unit is discouraged due to its ambiguity.	= 1 cd
candlepower (old, pre-1948)	cp	Varies and is poorly reproducible. Approximately 0.981 cd.	≈ 0.981 cd

Luminance

Luminance

Name of unit	Symbol	Definition	Relation to SI units
candela per square foot	cd/ft2	≡ cd/ft2	≈ 10.763910417 cd/m2
candela per square inch	cd/in2	≡ cd/in2	≈ 1550.0031 cd/m2
candela per square metre (SI unit); nit (deprecated)	cd/m2	≡ cd/m2	= 1 cd/m2
footlambert	fL	≡ (1/π) cd/ft2	≈ 3.4262590996 cd/m2
lambert	L	≡ (104/π) cd/m2	≈ 3183.0988618 cd/m2
stilb (CGS unit)	sb	≡ 104 cd/m2	= 104 cd/m2

Luminous flux

Luminous flux

Name of unit	Symbol	Definition	Relation to SI units
lumen (SI unit)	lm	≡ cd·sr	= 1 lm = 1 cd·sr

Illuminance

Illuminance

Name of unit	Symbol	Definition	Relation to SI units
footcandle; lumen per square foot	fc	≡ lm/ft2	= 10.763910417 lx
lumen per square inch	lm/in2	≡ lm/in2	≈ 1550.0031 lx
lux (SI unit)	lx	≡ lm/m2	= 1 lx = 1 lm/m2
phot (CGS unit)	ph	≡ lm/cm2	= 104 lx

Radiation – source activity

Radioactivity

Name of unit	Symbol	Definition	Relation to SI units
becquerel (SI unit)	Bq	≡ Number of disintegrations per second	= 1 Bq = 1/s
curie	Ci	≡ 3.7×1010 Bq	= 3.7×1010 Bq
rutherford (H)	rd	≡ 1 MBq	= 106 Bq

Please note that although becquerel (Bq) and hertz (Hz) both ultimately refer to the same SI base unit (s⁻¹), Hz is used only for periodic phenomena, and Bq is only used for stochastic processes associated with radioactivity.

Radiation – exposure

Radiation - exposure

Name of unit	Symbol	Definition	Relation to SI units
roentgen	R	1 R ≡ 2.58×10−4 C/kg	= 2.58×10−4 C/kg

The roentgen is not an SI unit and the NIST strongly discourages its continued use.

Radiation – absorbed dose

Radiation - absorbed dose

Name of unit	Symbol	Definition	Relation to SI units
gray (SI unit)	Gy	≡ 1 J/kg = 1 m2/s2	= 1 Gy
rad	rad	≡ 0.01 Gy	= 0.01 Gy

Radiation – equivalent dose

Radiation - equivalent dose

Name of unit	Symbol	Definition	Relation to SI units
Röntgen equivalent man	rem	≡ 0.01 Sv	= 0.01 Sv
sievert (SI unit)	Sv	≡ 1 J/kg	= 1 Sv

Although the definitions for sievert (Sv) and gray (Gy) would seem to indicate that they measure the same quantities, this is not the case. The effect of receiving a certain dose of radiation (given as Gy) is variable and depends on many factors, thus a new unit was needed to denote the biological effectiveness of that dose on the body; this is known as the equivalent dose and is shown in Sv. The general relationship between absorbed dose and equivalent dose can be represented as

H = Q · D

where H is the equivalent dose, D is the absorbed dose, and Q is a dimensionless quality factor. Thus, for any quantity of D measured in Gy, the numerical value for H measured in Sv may be different.

See also

• Accuracy and precision
• Conversion of units of temperature
• English units
• False precision
• Imperial units
• International System of Units
• Mesures usuelles
• Metric prefix (e.g. "kilo-" prefix)
• Metric system
• Natural units
• Rounding
• Significant figures
• United States customary units
• Units (software)
• Units conversion by factor-label
• Units of measurement

Notes and references

Notes

External links

• Statutory Instrument 1995 No. 1804 Units of measurement regulations 1995 From legislation.gov.uk
• How Many? A dictionary of units of measurement
• "NIST: Fundamental physical constants — Non-SI units" (PDF). (35.7 KB)
• NIST Guide to SI Units Many conversion factors listed.
• The Unified Code for Units of Measure
• Units, Symbols, and Conversions XML Dictionary
• Units, Symbols, Exchange, Equations, Human Readable
• Template:Dmoz
• Template:Dmoz