| Square feet (sq ft) | Square nautical miles (sq nmi) |
|---|---|
| 1 Square foot | 0.0000000270861924998 sq nmi |
| 2 Square feet | 0.0000000541723849997 sq nmi |
| 3 Square feet | 0.0000000812585774995 sq nmi |
| 4 Square feet | 0.000000108344769999 sq nmi |
| 5 Square feet | 0.000000135430962499 sq nmi |
| 10 Square feet | 0.000000270861924998 sq nmi |
| 20 Square feet | 0.000000541723849997 sq nmi |
| 25 Square feet | 0.000000677154812496 sq nmi |
| 50 Square feet | 0.00000135430962499 sq nmi |
| 100 Square feet | 0.00000270861924998 sq nmi |
| Reference | Square feet (sq ft) | Square nautical miles (sq nmi) |
|---|---|---|
| A sheet of A4 paper | 0.671345 sq ft | 0.0000000181842 sq nmi |
| A tennis court | 2807.23 sq ft | 0.0000760371 sq nmi |
| A football pitch | 76854.3 sq ft | 0.00208169 sq nmi |
| One hectare | 107639 sq ft | 0.00291553 sq nmi |
| Central Park, New York | 36704935 sq ft | 0.994197 sq nmi |
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.
The square nautical mile is a unit of area equal to 3,429,904 square metres, or about 3.43 square kilometres. Its symbol is sq nmi. It is the area of a square one nautical mile on a side, the nautical mile being defined as exactly 1852 metres. It is the working unit of everything that happens at sea and is measured across a surface rather than along a line.
Its usefulness comes from the definition of the nautical mile itself. One nautical mile is very nearly one minute of latitude, so a square nautical mile is close to a one-minute cell on a chart. That makes it the natural grid square for anything plotted on a nautical chart, because the unit and the graticule agree without any conversion, and a navigator can read distance and area off the same scale.
Maritime law is written in nautical miles and therefore accounted in square ones. Under the international law of the sea, a coastal state has a territorial sea of twelve nautical miles, a contiguous zone of twenty-four and an exclusive economic zone reaching two hundred. The resulting areas are vast: a state with scattered island possessions can control several million square kilometres of ocean, and comparisons between such claims are usually made after converting these figures to metric.
Search and rescue planning depends on the unit directly. A search area is defined in square nautical miles, and the time to cover it follows from the search vessel's speed in knots and the sweep width of its sensors, both of which are already in nautical units. Keeping the whole calculation in one system is what allows a coordinator to estimate coverage without stopping to convert anything.
Fisheries science and naval operations use it the same way. Fish stock density is reported per square nautical mile, survey transects are spaced in nautical miles, exercise and restricted areas are drawn as blocks of them, and aviation control zones over water are described in the same terms because aircraft also navigate in knots.
For conversion, one square nautical mile is 3.43 square kilometres, 1.32 square statute miles, or about 848 acres. The ratio to the statute mile is not intuitive, since the nautical mile is only about 15 per cent longer but the square is a third larger, which is the usual consequence of squaring a length ratio.
One square nautical mile equals 3,429,904 square metres, about 3.43 square kilometres, about 1.32 square miles, or about 848 acres.