Perch to Square Feet and Square Metres: the Sri Lankan Land Perch, Exactly

The perch is exact, and it is exact because it is a square rod. A rod, pole or perch is 16.5 ft, which is 5.5 yards, and the area perch is that length squared: 30.25 yd² and 272.25 ft². The yard has been 0.9144 m exactly since 1959, so the square yard is 0.83612736 m² exactly and the perch is 30.25 times that, 25.29285264 m², with no rounding anywhere in the chain. Four rods make a chain of 66 ft, ten chains make a furlong, and a furlong by a chain is the acre, 43,560 ft², which is why 160 perches make an acre and 40 make a rood. Sri Lanka's Survey Department prints the same figure: its Departmental Survey Regulations carry a table of area in perches against area in square metres, and the first row reads 1 perch, 25.2928 m², with 160 perches labelled 1A‑0R‑0P at 4,046.856 m². This page and that table agree to the last printed digit, and so they should, because both are the same definition.

The three roundings you will meet, and what each one costs. The commonest is “1 perch = 25 m²”, which is 1.16% low: on a 10‑perch plot it drops 2.93 m², about the floor of a small bathroom, and on an acre it drops 46.9 m². The second is “270 ft²”, 0.83% low, 22.5 ft² short on the same 10 perches. The third is “300 ft²”, which is 10.2% high and turns 10 perches into 3,000 ft² when the land is 2,722.5. The 25 m² figure is the one that travels furthest: a Jamaican property guide prints it in so many words, and Sri Lankan listings repeat it. None of these is wrong enough to notice on a sketch and every one of them is wrong enough to notice on a valuation, which is done per perch and therefore compounds the error by the price. The widget prints all three beside the exact figure so you can see which one a listing has used.

A deed carries the extent as acres, roods and perches, and the arithmetic back from square metres is division with remainders. To read a record, multiply: 0A‑1R‑20P is one rood of 40 perches plus 20, so 60 perches, 16,335 ft², 1,517.57 m². To write one, divide the area by 272.25 to get perches, take out whole roods of 40 and whole acres of four roods, and leave the fraction on the perches, which is where surveyors leave it: Jamaica's National Land Agency publishes adjudication notices describing parcels as “Ten Acres, One Rood, Two Perches and Seven‑Tenths of a Perch”, and the Sri Lankan regulations, when a court commission survey comes in with extent “shown as Acres, Roods and Perches”, say to consider one hectare as 2.4711 acres, which is the same acre this page uses to four places. That the record format is A‑R‑P is described here from those documents; no statute prescribing the format was read for this page, so treat the format as the convention of the record and the perch behind it as the definition.

Jamaica and England use the same perch; Ireland, Scotland and Cheshire did not. Jamaican titles are in the same acres, roods and perches, and the perch is the same imperial square rod. In England the Weights and Measures Act 1985 still defines the rood as 1,210 square yards and the acre as 4,840, which fixes the perch at 30.25 yd² the moment you grant forty to the rood; the word perch itself no longer appears in the Act. The old Irish plantation measure used a 7‑yard rod, so its perch was 49 yd² and its acre 7,840 yd², 62% larger than the statute acre. The Cheshire acre was 10,240 yd², which is a perch of 64 yd² from an 8‑yard rod. The old Scottish acre was 6,150.4 yd², so its square fall comes to 38.44 yd². These are offered here as history and are refused in the widget: a lease from 1780 in Ulster may be in any of three measures, and a calculator that silently applies the statute perch to it is not converting, it is guessing.

A perch of length is a different thing, and this page does not square it. The 16.5 ft rod is a distance, and a boundary in an old survey given as “12 perches” along a road is 198 ft of frontage, not 12 perches of land. Squaring a length quoted in perches produces a number in square perches that has nothing to do with the plot, and the reverse mistake, reading an area perch as 16.5 ft of frontage, is the same error facing the other way. The widget refuses the length option for that reason. The other trap is the price: Sri Lankan land is priced per perch, and the total is price per perch times perches, nothing more. The widget multiplies the two if you give it a price and also shows what that comes to per square metre and per square foot, but it assumes no currency and applies no duty, fee or tax; those are on the deed, not on this page.