Units of Measure index

Imperial Measures of Area


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This page gives Imperial units of area. Lengths (such as inches, feet, yards and miles) are on the length page and cubic lengths are on the volume. There is a quick convertor below which gives an answer rounded to 2 decimal places. The metric equivalents on this page are also all to 2 decimal places.
There are more advanced conversions on the tables page.

Enter value:   =   ?  

Well-known units - square inches, feet and yards
Land measurement - (square) rod, pole & perch, rood, acre, hide
Examination question
Silly units of area such as 'the size of Wales'.

Well-known units
conversion
A square inch is a square with sides of 1 inch. However 2 square inches is not a square with sides of 2 inches (which would be 4 square inches). It would be a rectangle with sides 2 inch and 1 inch. So it is necessary to learn a different table for square units.
MetricTable
square inch6.45 sq cm12 x 12 inches = 1 square foot
144 square inches = 1 square foot
see inch
square foot929.03 sq cm3 x 3 feet = 1 square yard
9 square feet = 1 square yard
see foot
square yard8361.27 sq cm22 x 22 yards = 1 square chain
484 square yards = 1 square chain
see yard
square chain404.69 sq m10 x 10 chains = 1 square furlong
100 square chains = 1 square furlong
see chain
square furlong40468.56 sq m8 x 8 furlong = 1 square mile
64 square furlong = 1 square mile
see furlong
square mile2589988.11 sq msee mile


Land measurement
conversion
MetricTableInformation
(square) rod, pole or perch25.29 sq m1 pole x 1 pole = 1 (square) pole
30.25 square yards = 1 (square) pole
40 (square) poles = 1 rood
Rod, pole and perch are rather complicated. First, they are different names for the same unit of length, which is five and a half yards (see length page). To shorten the explanations, I use one unit rather than all three. Next, they could also be used as a unit of area. So a 10 perch allotment would be 5.5 yards wide by 55 yards long, or 10 square perch. To make my explanations clear, I say '(square) rod' to mean rod as a unit of area.
rood1011.71 sq m1210 square yards = 1 rood
40 (square) poles = 1 rood
1 furlong x 1 pole = 1 rood
4 roods = 1 acre
Old records of land mention areas measured in '... A, ...R, ...P'. This will be acres, roods and (square) poles or perch.
Old American records refer to a 'goad', which may be the same as a rood, although a goad may be other sizes as well.
acre0.4 hectares4840 square yards = 1 acre
1 furlong x 1 chain = 1 acre
10 square chains = 1 acre
4 roods = 1 acre
640 acres = 1 square mile
An acre is a conventional measure of area. It was defined in the time of Edward I (1272-1307) and was supposed to be the area that a yoke of oxen could plough in a day. Acre is derived from the Latin for field, but the common field system of medieval times in Britain was ten acres. An acre is a furlong long and a chain wide. In fact, an archaic word for furlong was 'acre-length' and for chain 'acre-width'. See the length page for furlong and chain.
If you want to visualise an acre, it's a square with sides of nearly 70 yards (or 64 metres). A hectare is about two and a half acres.
The Scottish and Irish used to have different values for their acres. The Scottish acre was 6150.4 square yards and the Irish acre was 7840 square yards.
Statutory Instrument 1995 No. 1804 allows the use of the acre for land registration.
hide?40 hectares?100 acres = 1 hide A hide was enough land to support a house-hold, usually between 60-120 acres (24-48 hectares). A hide of good land was smaller than that of poor quality. Hides are used in the Doomsday Book. However, I have a reference of a hide as 100 acres.
A correspondent wrote: An oxgang was viking measure used in the Doomsday Book, and was the area of land that an ox could plough in one season. Since oxen were usually used in teams of eight, the area that eight ox could plough was called a bovate, or carucate. So an oxgang was about 15 acres, and a bovate was 100-120. Just to make it more awkward, parts if England not under Danelaw used the virgate, which was twice the size of an oxgang (because you used two ox instead of one), and a carucate was then known as a Hide.



Examination question
conversion

Here is an old examination question for candidates for admittance to American High School:

Multiply 17 A, 3 R, 28 rds, 19 yds, 8 ft, 97 in, by 9

I think that A are acres, R are roods, rds are (square) rods, yds are (square) yards, ft are (square) feet and in are (square) inches. The square units are implied, otherwise the question doesn't make sense!

So how would we do this problem? First list all the units with the smallest first (because a smaller unit will cascade into a bigger unit). Multiple each unit separately - the answer is under Multiple. But this needs to be reduced. If you have an answer of over 144 square inches, then you need to 'take out' some square feet until you get under 144 square inches, and add those square feet into the next line. I've listed the relevant table in brackets at the end of the line to remind me.

SumMultipleReduce unitsTable
97 square inches x 9 =873 sq in873 sq in / 144 = 6 sq ft 9 sq in9 sq in(144 sq in = 1 sq ft)
8 square feet x 9 =72 sq ft(72 + 6) sq ft / 9 = 8 sq yd 6 sq ft6 sq ft(9 sq ft = 1 sq yd)
19 square yards x 9 =171 sq yd(171 + 8) sq yd / 30.25 = 5 sq rod 27.75 sq yd27.75 sq yd(30.25 sq yd = 1 sq rod)
28 square rods x 9 =252 sq rod(252 + 5) sq rod / 40 = 6 rood sq 17 rod17 rod(40 sq rod = 1 rood)
3 roods x 9 =27 roods(27 + 6) rood / 4 = 8 acres 1 rood1 rood(4 rood = 1 acre)
17 acres x 9 =153 acres(153 + 8) acres = 161 acres161 acres
That gives 161 acres 1 rood 17 rod 27.75 sq yd 6 sq ft 9 sq in. But we haven't finished yet. There isn't a whole number of square yards to a square rod, and the answer has a spare 0.75 square yards. That needs reducing as well, but as it's less than one, it needs reducing the other way. 0.75 square yards = 6 square feet 108 square inches. Add those in to the answer. But now we have (6 + 6 square feet) which is more than a square yard. Bother. So 27.75 sq yd 6 sq ft 9 sq in = (27 + 1) sq yd 3 sq ft 117 sq in (at least we didn't have to do anything to the inches!) Now combine that with the whole answer and use the original abbreviations for the units and we have (I hope!)

161 A, 1 R, 17 rds, 28 yds, 3 ft, 117 in      (See calculator to check this.)

Phew! Children were expected to do such sums without calculators, or having the conversion tables in front of them, although we were told to "show our working" so a slight slip would not waste all our work and might still gain us a little credit. Some people think that education used to be better for such mental arithmetic. I doubt it. We do now have calculators, so why not use them, and I've seen modern children confidently handle decimals, percentages, angles, symmetry, tessellations and nets for three dimensional shapes at half the age that I did (in fact we never got on to symmetry).

If on the other hand you want to try your own hand at such problems, here is another question, this time using weight.

Divide 45 T, 17 ewt, 1 qr, 24 lbs, 12 oz, 8 dr, by 8

Here we have tons, a misprint for hundredweight (cwt), quarters (usually abbreviated as qtr in Britain), pounds, ounces and drams. I leave the sum as an exercise for the reader!




Silly units of area

A lovely letter in New Scientist said "The proper units for large areas, such as those of giant icebergs and hurricanes, are the Wales (metric) and the Delaware (imperial). The conversion rate is approximately 3.215 Delawares to the Wales... Measurements of height is, of course, in Eiffeltowers and Empirestatebuildings (1.368 Eiffeltowers to the Empirestatebuilding)." Here is a good website which calculates areas in this unit! I think that the Wales has replaced the Isleofwight, which used to be the standard unit. I have also spotted the Luxembourg as a measure of icebergs as well. This is, of course, rather a large area. A football pitch is often used for small areas, and Cambridge has been used for medium areas. As a very rough approximation (and that is all these units are!)

5000 Football Pitches = 1 Cambridge

500 Cambridges = 1 Wales