acre

 Share 

See also Cheshire acre, Churchland acre, Cornish acre, Cunningham acre, Forest acre, Devonshire acre, Herefordshire acre, Inverness acre, Irish acre, Lancashire acre, Leicester acre, Rhynland acre, Scottish acre, Somersetshire acre, Staffordshire acre, Welsh acre, West Derby acre, Westmoreland acre, Wiltshire acre, Woodland acre

1

The statute acre, in the English-speaking world, before 8th – 21st century, the principal unit of land area. At one time many different acres existed in England (notice the see-also list above), and this acre was often called the “statute acre”, to indicate it was the one established by law, at least as early as the 14th century. In places like the United States, where the statute acre is overwhelmingly predominant, the word “statute” is usually omitted. The (statute) acre is:

comparison of acre with hectare

In the United States, because the acre is a land measure it is currently based on the U.S. survey foot and not on the international foot. One acre is about 4,046.873 square meters.

A square plot of ground 208.7 feet on a side will cover an acre. An American football field, 360 feet by 160 feet, is about 1.3 acres; 12 high school basketball courts are a little more than 1 acre. Here's a way for city dwellers to use a Google map of their neighborhood to get a feel for how big an acre is.

The acre is not a measure of surface area on the actual surface of the earth, but on an imaginary, hill-less, standardized ellipsoid. That result comes from using only strictly horizontal dimensions in calculating acreage. For more information, please see the FAQ.

The rest of this entry on the statute acre contains the following sections:

B. Converting acres to other units

thumbnail of chart to convert between acres and hectares

Download a printable, letter-size chart (as seen at the right) to convert between acres and hectares visually.

Converting between acres and hectares

  is approximately equal to   

 

The calculator below gives the number of acres in a rectangular field. Or, enter the acreage and a width, and the length will be calculated.

Calculate acreage from lengths of sides

Choose the in which you will measure lengths:

 feet  by    feet  =   

Sometimes when sowing seed or applying fertilizer to hilly ground, it is useful to know the actual surface area, as if the land were flat. The calculator below makes a rough estimate based on the slope of the ground.

Estimate surface area

Grade:  in  , OR %

:  acres 

, as if it were flat land “acres”

 

C. Origin of the acre: 4 by 40, sized for ploughing

The acre was originally the amount of land that could be plowed in a single day with oxen, or actually, what could be done by midday, since refueling took all afternoon (the oxen had to be put out to pasture). Similar units of land area are found wherever animals are used for plowing. The German Morgen and Roman jugerum had much the same meaning.

Like many units of land area, the acre was first thought of as a piece of land having certain fixed dimensions. An acre was 40 perches long and 4 perches wide. The length of the acre, 40 perches, was roughly the distance a team of oxen could plow before needing a breather (this furrow-long became the furlong, 220 yards). Ploughmen prefer long furrows, because turning a team of oxen is a cumbersome process.

diagram of the rood

A strip 40 perches long and 1 perch wide was called a rood (not to be confused with the rod, a name from the Saxon gyrd used by the 13th century as a synonym for the perch.)  So 1 acre was 4 roods. Not until much later (the 16th century, according to R. D. Connor) did most people begin to think of the acre as so many square feet or square rods.

In actual use in the Middle Ages the size of the acre varied greatly, generally being larger in poor land than in good. In some contexts it was almost synonymous with “small holding.”

Another complicating factor is that there were a variety of perches. As you can see, the area of the acre depends on the length of the perch.

The king's rod or perch, however, remained constant for eight centuries at 16½ feet, and that perch set the size of the statute acre.

D. The end of the acre

In 1979, Council Directive 80/181/EEC of the European Community1, governing standardization on metric units in the European Union, included an exception that permitted Ireland and the United Kingdom to continue using the acre for a limited time. The Council was supposed to set an end date by 31 December 1989. In 1989, the directive was amended to leave the setting of the date to the U.K. and Ireland. Finally in 2007 the exception was allowed to expire2, since Ireland had finished converting its land registration system to meters by the end of 1998, and the U.K. sometime afterwards. Beginning 1 January 2010 the acre could no longer be used in the U.K. for any economic, public health, public safety or adminstrative purpose.

In Australia, the acre was abandoned in 1987.

In New Zealand, the Weights and Measures Act 1987 provided that "Weights and measures of the metric system shall, except as expressly provided in this Act, be the only weights and measures used for trade in New Zealand," and the hectare is listed in the schedule of units. The hectare is currently (2012) in use, but in real estate advertisements, for example, it is often supplemented by the size in acres.

In Canada, the Weights and Measures Act 1985 permits use of the acre and the hectare, as well as certain old French units for land in Quebec granted under seigneurial tenure.

1. Council Directive of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC. On the web at http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1980L0181:19791221:EN:PDF

2. Proposal for a Directive of the European Parliament and of the Council amending Council Directive 80/181/EEC on the approximation...  On the web at http://europa.eu/eur-lex/lex/LexUriServ/LexUriServ.do?uri=COM:2007:0510:FIN:EN:PDF See item 6.

 

E. Frequently asked questions about the acre

1. What are the dimensions of the acre?

“I just wanted to know what are the dimensions of an acre—how many feet wide and long?”

“If an acre is a square or rectangular why doesn't anybody on the web know what the measurements are in feet, not sq. feet. I have looked in about 1000 different places and no one has an answer that simple.”

“If I am to measure an acre as length x width what would that measure be? I have looked up many sites but cannot find this measurement.”

Since medieval times the acre hasn’t had any specific dimensions. It is purely an area of 43,560 square feet. The two sides of a 1-acre rectangular lot can be any lengths as long as multiplying one by the other gives 43,560 (if they are measured in feet). For example, imagine a sidewalk 5 feet wide. If it were (43560 ÷ 5 = ) 8712 feet long it would take up an acre, a long skinny acre. On the other hand, if the 1-acre lot were a square, its sides would be only 208.7 feet long.

 

2. What is the perimeter of an acre?

“Can you tell me [if the distance around] one acre of land is more than a mile? I want to purchase property, but I want the distance around the property to be at least 1 mile.”

Because the acre is a measure of area, it has no specific perimeter. For example, using the examples in question one, the perimeter of the long, skinny sidewalk acre would be 17,434 feet (more than 3 miles), but the perimeter of the square acre would be 835 feet. If you don’t know the shape of the lot you can’t determine the perimeter.

 

3. How are acres measured on hillsides?

“If I buy a hill, it being sold as 242 acres, how are the acres measured? Are they as if the hill were cut off and the land was level? Or up one side of the hill and down the other as if it were covered with a blanket and then the size of the blanket was measured?”

It's as if the hill were cut off and the land was level. To quote from an old authoritative surveying text, by two professors at MIT:

Horizontal Lines. -- In surveying, all measurements of lengths are horizontal or else are subsequently reduced to horizontal distances. As a matter of convenience, measurements are sometimes taken on slopes, but the horizontal projection is afterward computed. The distance between two points as shown on a map then is always this horizontal projection.

Charles B. Breed and George L. Hosmer.
The Principles and Practice of Surveying, Vol 1. 
New York: John Wiley & Sons, 1908.

F. Sources

1

Statutum de Admensuratione Terre
Statute for the Measuring of Land

[Undated but attributed to the 33rd year of Edward I (1305), though the substance is older. The great bulk of the statute is given over to a lengthy list of pairs of lengths and widths of fields which, multiplied, make 160 square rods (one acre), beginning with 10 rods by 16 rods and ending at 80 rods by 2 rods. It then concludes, here translated from the Latin:]

And Be it Remembered, That the Iron Yard of our Lord the King, containeth three feet and no more. And a Foot ought to contain Twelve inches, by the right measure of this Yard measured; to wit, the Thirty-Sixth part of this Yard rightly measured maketh one Inch, neither more nor less. And Five Yards and a half make one Perch, that is Sixteen Feet and a half, measured by the aforesaid Iron Yard of our Lord the King.

Statutes of the Realm, vol. 1, page 206.

2

Some men will tell you that a plough cannot work eight score or nine score acres yearly, but I will show you that it can. You know well that a furlong ought to be forty perches long and four wide, and the king's perch is sixteen feet and a half; then an acre is sixty-six feet in width.

Walter of Henley's Husbandry, page 9. Written (in French) about 1280.

Because acres are not all of one measure, for in some countries they measure by the perch of eighteen feet, and in some by the perch of twenty feet, and in some by the perch of twenty-two feet, and in some by the perch of twenty-four feet,…

Anonymous. Seneschaucie, page 69. Probably written in the 1270's.
Elizabeth Lamond, editor and translator.
Walter of Henley's Husbandry, together with an anonymous Husbandry, Senschaucie and Robery Grosseteste's Rules.
London: Longmans, Green and Co., 1890.
For a more recent version, see
Dorothea Oschinsky.
Walter of Henley and Other Treatises on Estate Management and Accounting.
Oxford: Clarendon Press, 1971.

3

¶ The Fourme and the Mesur to mete Land by.

... V. yardis di. make a perche in Londo to mete lande by, and that perch is xvi. fote di. longe. In dyuers odur placis in this lande they mete grounde by pollis gaddis and roddis som be of xviij. foote som of xx. fote and som xxi. fote in lengith, but of what lengith soo euer they be C.lx. perches make an akir, for as a mark of English monei conteyneth an C. lx. pence soo euery akir lande conteyneth C. lx. perchies, and as a noble conteyneth lxxx. pense soo half an aker lade conteyneth Ixxx. perchis, etc., and as the half a noble conteyneth xl. d'. soo a roede lande coteyneth xl. perchi etc., and a perche of grounde shal coteyngne I lengith of the perche euery wey i the maner of a cheker soo y it be as loge as brode.

Five and a half yards make a perch in London to measure land by, and that perch is 16½ feet long. In various other places in this land they measure ground by poles, gads and rods; some are 18 feet, some 20 feet and some 21 feet in length, but of what length soever they be 160 [square] perches make an acre, for as a mark of English money contains 160 pence so every acre of land contains 160 [square] perches, and as a noble contains 80 pence so half an acre of land contains 80 [square] perches, etc., and as half a noble contains 40 pence, so a rood of land contains 40 [square] perches, etc. A [square] perch of ground shall contain the length of a perch in both directions, in the manner of a square, so it is as long as broad.

The Customs of London, otherwise called Arnold’s Chronicle.
London: Printed for F. C. and J. Rivington; T. Payne; etc., 1811.
Page 173.
The first edition appeared in Antwerp around 1502.

G. Resources

A list of some local values of the acre in Britain in the 18th century is given in the Second Report of the Commissioners... (1820, page 5).


2

In England, 11th – 19th century, a unit of length = 4 perches or rods, = 66 feet, the width of the original acre. In medieval documents it usually, if not always, appears as part of a qualifying phrase that indicates that the width is meant. For example:

“three acres wide”

#781 in Kemble, Codex Diplomaticus Aevi Saxonici.

“..iii acera bræda...”

Legis Æðelstan, IV 5.

“...ix acrae latitudine...”

Legis Hen I, cap. xvi.

In the 17th century this distance became the length of the surveyor's chain. This length is also the distance between wickets in cricket, and the width of the strip of land that could be acquired by eminent domain for a road in the less-developed parts of the British Commonwealth.

The acre survived as a 66-foot unit of length into the 19th century in Bedfordshire and Buckinghamshire. In Derbyshire it could be either 84 or 96 feet, while in Yorkshire as a unit of length the acre was 84 feet.1

1. Second Report. Page 6.

3

In England the acre was also a unit of tax assessment. As such, it was not strictly related to the actual dimensions of the property. The following terms are mostly used by modern scholars:

geld acre

In Anglo-Saxon and Norman England, the acre as a unit of assessment of the king's geld, the crown tax. So for example, a person down in the tax rolls as the holder of 40 geld acres might, but probably didn’t, hold 40 areal acres (6400 square rods) of land. If the tax were, say, 2 shillings per acre, he owed 80 shillings, regardless of the actual size of his property.

ware acre

In East Anglia, 1/120th of a carucate (also in this case not an areal unit), a unit of assessment of taxes due the king that were to be paid in something other than money (for example, in fodder for horses).

4

In Normandy, 13th – 15th centuries?, a unit of land area = 160 square perches (each perch of 22 pieds), = 77,449 square pieds, about 8172 square meters.  This unit was probably brought back from England to Normandy in the years following the Norman invasion. Local variations were plentiful, varying with the length of the perch.

sources

H. Navel (Commandant).
Recherches sur les anciennes mesures agraires normandes. Acres, vergées et perches.
Caen: Jouan et Bigot, 1932.

home | units index | search |  to email Sizes drawing of envelope |  acknowledgements | 
help | privacy | terms of use