Whole-Acre Reference / Sheet 01
1 Acre = 43,560 sq ft
The chain-and-furlong constant. One surveyor's chain (66 ft) multiplied by one furlong (660 ft) equals 43,560 square feet, the international acre formalised by the 1959 IYPA. About 90 percent of a US football field. The unit that has organised American land for 250 years.
Square Feet
43,560
international ft2
Square Metres
4,046.86
m2
Hectares
0.4047
ha
Derivation: 1 chain (66 ft) × 1 furlong (660 ft) = 43,560 sq ft, exactly. Per Edmund Gunter (1620) and ratified by the 1959 International Yard and Pound Agreement.
Sheet 02 · The Chain-and-Furlong Story
Why 43,560 and not some round number
The acre is one of the few units of measure in modern use that predates rational design. It was not invented in a committee. It was a working unit for ploughmen, surveyors, and tax assessors that hardened into law over centuries. The acre originally meant the area one yoke of oxen could plough in one day, which depended on the soil, the team, and the daylight, but in medieval English practice came to mean a long narrow strip 4 rods wide by 40 rods long. A rod (also called a perch or pole) was 16.5 feet, so the medieval acre was 66 ft by 660 ft, exactly the same dimensions as the modern one.
The chain-and-furlong derivation came from Edmund Gunter, an English mathematician and clergyman who in 1620 invented a 66-foot iron chain divided into 100 links. The chain was designed for surveyors to use in the field: easy to lay flat across uneven ground, divisible into convenient decimal subunits (one link is 7.92 inches), and sized so that 10 chains by 10 chains equals exactly 100,000 square links, or 10 acres. The furlong (literally the "furrow long," the standard length of a medieval ploughed strip) is 10 chains, or 660 feet. One chain by one furlong is 66 ft by 660 ft, equal to 43,560 sq ft, equal to one acre.
The Gunter chain became the standard surveying tool of the British Empire, and it crossed the Atlantic with American colonisation. The US Public Land Survey System (PLSS), enacted by the Land Ordinance of 1785, divided the new western territories into townships of 6 miles by 6 miles, sections of one square mile (640 acres), quarter sections of 160 acres (the original Homestead Act parcel), and quarter-quarter sections of 40 acres. Every one of these units derives from the chain-and-furlong arithmetic. The PLSS still organises the property records of 30 US states (everything west of Pennsylvania except Texas and parts of the original colonies) and remains the legal basis for most western land descriptions.
The 1959 International Yard and Pound Agreement, signed by the US, UK, Canada, Australia, New Zealand, and South Africa, defined the international foot as exactly 0.3048 metres, which made the international acre exactly 4,046.8564224 m2. The historic US survey foot (1200/3937 m, used in PLSS field measurements) was retained for federal land records until October 1, 2022, when the National Geodetic Survey deprecated it in favour of the international foot for all new federal surveys. The difference is small (about 3.22 sq ft per 640 acres), but historically significant for very large parcels.
Sheet 03 · What 1 Acre Looks Like
Real-world references for 43,560 square feet
- · About 90 percent of a US football field: the field with end zones is 57,600 sq ft (1.32 acres). 1 acre is roughly the field of play minus a few yards.
- · About 75 percent of a soccer pitch: a FIFA standard pitch is 60,000 to 80,000 sq ft. 1 acre is roughly two thirds of a top-tier pitch.
- · About 9.3 NBA basketball courts: at 4,700 sq ft each.
- · About 16 doubles tennis courts: at 2,808 sq ft each.
- · About 121 standard parking spaces: at 360 sq ft per car including drive aisles.
- · About 22 typical 2,000 sq ft American houses: if you laid the building footprints next to each other without setbacks.
- · 1/640th of a square mile: the PLSS section, the standard farm-country reference.
- · 1/24th of Disneyland Park, California: the park is 85 acres total.
- · 1/843rd of Central Park, NYC: the park is 843 acres total.
- · 1/109th of Vatican City: the smallest sovereign state in the world is 109 acres.
Sheet 04 · The Acre in Modern Use
Where the unit still does work
The acre is the dominant unit for residential and agricultural land in the US, the UK (alongside hectares), Canada, India, and the historic British Empire countries. US Department of Agriculture cropland reporting uses acres as the primary unit (the 2022 Census of Agriculture reported 880 million acres of US farmland). Real-estate listings in the US use acres for parcels above roughly 0.5 acres and square feet for smaller urban lots. State conservation easements, federal forest land, and Bureau of Land Management public land are all reported in acres.
Outside North America, the hectare (10,000 sq m, or 2.471 acres) has largely replaced the acre in EU agricultural reporting since the 1980s. The UK retains acres in legal property descriptions (the Weights and Measures Act 1985 lists the acre as a legally recognised unit) but uses hectares in most government statistics and EU-aligned reporting. Australia, Ireland, and Scotland have similar bilingual conventions: hectares for official statistics, acres for everyday descriptions of farms and rural properties.
One commercial-acre convention deserves a footnote. The commercial acre (about 36,000 sq ft, 82.6 percent of a standard acre) was historically used in some US cities to account for streets, sidewalks, and alleys when subdividing a parcel into lots. It is not a legal or SI unit and does not appear in modern legal descriptions. If a real-estate contract uses the term "commercial acre" without specifying square footage, ask for clarification before relying on the area for any calculation.