| Square miles (sq mi) | Square feet (sq ft) |
|---|---|
| 1 Square mile | 27878400 sq ft |
| 2 Square miles | 55756800 sq ft |
| 3 Square miles | 83635200 sq ft |
| 4 Square miles | 111513600 sq ft |
| 5 Square miles | 139392000 sq ft |
| 10 Square miles | 278784000 sq ft |
| 20 Square miles | 557568000 sq ft |
| 25 Square miles | 696960000 sq ft |
| 50 Square miles | 1393920000 sq ft |
| 100 Square miles | 2787840000 sq ft |
| Reference | Square miles (sq mi) | Square feet (sq ft) |
|---|---|---|
| A sheet of A4 paper | 0.0000000240812 sq mi | 0.671345 sq ft |
| A tennis court | 0.000100695 sq mi | 2807.23 sq ft |
| A football pitch | 0.00275677 sq mi | 76854.3 sq ft |
| One hectare | 0.00386102 sq mi | 107639 sq ft |
| Central Park, New York | 1.31661 sq mi | 36704935 sq ft |
The square mile is a unit of area equal to 640 acres, or 2.589988 square kilometres. Its symbol is sq mi. It is the area of a square one mile on a side, and it is the unit in which American and British counties, cities, parks and disaster zones are described. Its equivalence to exactly 640 acres is not an accident but the foundation of how much of North America was laid out.
The United States Public Land Survey, begun in 1785, divided the western territories into townships of six miles square, each containing thirty-six sections of one square mile. A section holds 640 acres, a quarter section 160, and a quarter of that 40. Those numbers ran through homestead law, land sales and inheritance for a century, and they are still visible from the air in the grid of roads that follows section lines across the Midwest.
Because the survey made the square mile a legal container rather than a mere measurement, it shaped settlement patterns. A quarter section was considered the amount of land a family could work, so farms across the plains came in multiples of 160 acres, and the mile spacing of section-line roads set how far apart towns, schools and grain elevators could usefully sit.
Today its everyday use is descriptive. Population density in American statistics is people per square mile, so around 92 for the country as a whole against nearly 30,000 for Manhattan. Wildfire extent, flood inundation, national park size and metropolitan area are all reported the same way, and British usage matches it for county and national park areas even where other measurements have gone metric.
Converting is straightforward if the factor is remembered: one square mile is 2.59 square kilometres, and one square kilometre is 0.386 square miles. The relationship is not intuitive because it is the square of the length ratio, so a place described as ten times larger in square miles is only about 3.2 times larger in linear extent.
Its awkwardness shows when the three imperial land units are chained. A square mile is 640 acres, an acre is 4840 square yards, and a square yard is nine square feet, so going from a square mile to a square foot means multiplying by 27,878,400. That figure is exactly why land and building are measured with different units even inside the same system.
One square mile equals 640 acres, about 2.59 square kilometres, 259 hectares, or 27,878,400 square feet.
The square foot is a unit of area equal to 144 square inches, or 0.092903 square metres. Its symbol is sq ft, sometimes written ft². It is the area of a square one foot on a side, and it is the unit in which property is bought, sold and rented across the English-speaking world and in several places that are otherwise entirely metric.
Real estate is its home. American and British homes are advertised by their floor area in square feet, and commercial space is let at a rent per square foot per year, which is the standard way of comparing one building or one city with another. A one-bedroom flat runs to about 500 square feet, a family house between 1500 and 2500, and an office desk with its share of circulation is reckoned at 150 to 200.
Its reach goes beyond countries that use imperial units generally. Apartments in India are sold by the square foot despite the country being metric in every other respect, and Hong Kong quotes flat sizes and prices the same way, which produces some of the highest per-square-foot figures on earth. In both cases the unit survived because the property market adopted it before metrication and never had a reason to change.
Building trades use it for materials and for capacity. Flooring, carpet, tile, plasterboard and insulation are priced by the square foot in North America; roofing has its own multiple, the square, equal to one hundred square feet; and air conditioning is sized in British thermal units per square foot of conditioned space. Leather is sold by the square foot in the United States where European tanneries use square decimetres.
The conversion to metric is exact but inconvenient. Since the foot is defined as exactly 0.3048 metres, one square foot is exactly 0.09290304 square metres, and one square metre is 10.7639 square feet. Neither figure is memorable, so converted property listings often show suspiciously round numbers in one system and awkward ones in the other, which is a reliable sign of which unit the original was written in.
Above it, land moves to the acre at 43,560 square feet, and below it the square inch takes over at one hundred and forty-fourth of the value. That factor of 144 rather than 100 is what makes mental arithmetic in imperial areas harder than in metric ones.
One square foot equals 144 square inches, about 0.0929 square metres, or about 0.1111 square yards.