Poise (unit)

The poise (symbol P; English: /ˈpɔɪzˌˈpwɑːz/) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units. It is named after Jean Léonard Marie Poiseuille.

$1~{\text{P}}=0.1~{\text{kg}}\cdot {\text{m}}^{-1}\cdot {\text{s}}^{-1}=1~{\text{g}}\cdot {\text{cm}}^{-1}\cdot {\text{s}}^{-1}=1~{\text{dyne}}\cdot {\text{s}}\cdot {\text{cm}}^{-2}.$

The analogous unit in the International System of Units is the pascal-second (Pa·s):

$1~{\text{Pa}}\cdot {\text{s}}=1~{\text{N}}\cdot {\text{s}}\cdot {\text{m}}^{-2}=1~{\text{kg}}\cdot {\text{m}}^{-1}\cdot {\text{s}}^{-1}=10~{\text{P}}.$

The poise is often used with the metric prefix centi- because the viscosity of water at 20 °C is almost exactly 1 centipoise. A centipoise is one hundredth of a poise, equal to one millipascal-second (mPa·s) in SI units (1 cP = 10⁻³ Pa·s = 1 mPa·s).

The CGS symbol for the centipoise is cP. The abbreviations cps, cp, and cPs are sometimes seen.

Liquid water has a viscosity of 0.00890 P at 25 °C and a pressure of 1 atmosphere (0.00890 P = 0.890 cP = 0.890 mPa·s).

See also

• Viscosity