Talk:Square kilometre

Value in acres

I was checking the values listed on this page. The page currently says that 1 sq km equals 247.105383 acres.

The GNU units program gives 247.10439 acres

The National Oceanographic Data Center say 247.105381 acres [1]

The Google calculator also says 247.105381 acres [2]

I think 247.105381 is probably right. It is a pretty minor thing but it would be good to get it right. I will try to do some more checking, but welcome any comments from others. -- Popsracer 11:21, 29 Sep 2003 (UTC)

1 sq km = 1,000,000 sq m

0.3048² sq m = 1 sq ft

16.5² sq ft = 1 sq rod

160 sq rods = 1 acre

1 sq km = 247.105381467 acres

er... I think... Evil saltine 11:44, 29 Sep 2003 (UTC)

GNU Units assumes the U.S. survey acre instead of the international acre. The figure 247.105383 has an error in its last digit. -- Indefatigable 16:58, 30 Sep 2003 (UTC)

That's why the metric system is the best. A metre is a metre is a metre, and a kilometre is a kilometre is a kilometre. None of this business of having to remember whether you're British or American, land-based or nautical, civilian or military, and so on. JIP | Talk 18:30, 22 September 2008 (UTC)

Oh yeah. metric system is the best.78.106.148.243 (talk) 16:15, 3 February 2009 (UTC)

You'll certainly get a 'squire deal' of of this measurment, sir! --Arma Martin 3nd 03:34, 26 January 2007 (UTC)

Trouble is that we have two slightly different values for both the acre and the square mile, one for the International measurements and the other for the US Survey measurements. The text will have to be changed to reflect this fact. Michael Glass (talk) 06:28, 12 June 2012 (UTC)

Proposal to change the text to reflect the difference between the International and US Survey measurements

At the moment, the text reads:

• 0.386302 square miles
• 247.105381 acres

and

• 1 square mile = 2.58998811km²
• 1 acre = 0.004047km², 0.4047ha or 4047 m²

2.47 acres/ha

No source is given for these figures, and the text does not reflect the fact that there are in fact two very slightly different miles in use in the United States. My proposal is to use the figures from unitconversion.org. This would make the text read as follows:

• 0.386102159 square miles (International)
• 0.386100614 square miles (US Survey)
• 247.105381467 acres (International)
• 247.104393047 acres (US Survey)

and

• 1 square mile (International) = 2.58998811km²
• 1 square mile (US Survey) = 2.58999847km²
• 1 acre (International) = 0.004046856km², 0.4046856ha or 4046.856m²
• 1 acre (US Survey) = 0.004046873km², 0.4046873ha or 4046.873m²

This, of course presumes that UnitConversion.org is right. What do others think? Michael Glass (talk) 12:39, 13 June 2012 (UTC)

Michael Glass (talk) 05:09, 17 June 2012 (UTC)

Obviously the US survey foot was preserved so it could continue to be used, as one option, to report the results of geodetic surveys. The National Geodetic Survey and its predecessor organizations, right back to the Survey of the Coast organized in 1807 used metric units, but some of the results, such as the State Plane Coordinate System were made available in survey feet. Today the difference is only significant for state plane coordinates, where the origin is many miles from the points being surveyed. Since areas are based on the relative location of the points defining the parcel, the differences in using survey feet or international feet to compute acres or square miles would be insignificant compared to the uncertainty in the area. So I see no need to use or mention US survey feet in this article. Jc3s5h (talk) 20:19, 19 June 2012 (UTC)

Speaking only of US practice, I don't think you're quite right here; equally important to the geodetic and coast surveys were the Land Survey which was the basis of much land ownership and was firmly rooted in traditional units and the Geological Survey, which employed both metric and traditional units. Prior to 1959 the US inch was defined as 1/39.37 meters and the survey foot was correspondingly 1200/3937 meters. In 1959 the relations between metric and traditional units were redefined, with the yard exactly exactly 0.9144 meters, the foot 0.3048 meters, and the inch 25.4 mm. Although US surveys used metric units, when those surveys were related to customary units, the old conversion was consistently used until 1959, so rigorously speaking, converting square kilometers to acres or square miles should use the conversion of feet to meters being used at that time.

Before making such a change, we should look into whether British practice made significant use of traditional units. I know their early maps were denominated in inches, but they made the change to metric mapping (and land survey) earlier than the US. Since the international foot was midway between US and British units, if their case is relevant to survey measurements it will lead to further complications. SteveMcCluskey (talk) 04:07, 21 June 2012 (UTC)

Thank you for the two comments above. Actually my first concern was about accuracy. The figures in the article at the moment are unsourced and are significantly different from the measurements given in UnitConversion.org.

• My first concern is whether UnitConversion.org is a reliable source for the information.

Before making any change I think it is necessary to determine this question first. Michael Glass (talk) 13:21, 21 June 2012 (UTC)

I don't know if UnitConversion.org is a good source or not. I do not see any citation to it in the article. In my view the best source for US measurements is the NIST Handbook 44. This is the document relied upon by state weights and measures departments. If your measuring device used in commerce does not meet the requirements in this handbook, state weights and measures officials will seize your device and fine you. Jc3s5h (talk) 13:32, 21 June 2012 (UTC)

It's a 497 page document but it doesn't seem to refer to square kilometres, perhaps because land measurements of that size are not sold very often in the United States. Is there any other source? Michael Glass (talk) 12:21, 23 June 2012 (UTC)