| Square feet (sq ft) | Square meters (m²) |
|---|---|
| 1 Square foot | 0.09290304 m² |
| 2 Square feet | 0.18580608 m² |
| 3 Square feet | 0.27870912 m² |
| 4 Square feet | 0.37161216 m² |
| 5 Square feet | 0.4645152 m² |
| 10 Square feet | 0.9290304 m² |
| 20 Square feet | 1.8580608 m² |
| 25 Square feet | 2.322576 m² |
| 50 Square feet | 4.645152 m² |
| 100 Square feet | 9.290304 m² |
| Reference | Square feet (sq ft) | Square meters (m²) |
|---|---|---|
| A sheet of A4 paper | 0.671345 sq ft | 0.06237 m² |
| A tennis court | 2807.23 sq ft | 260.8 m² |
| A football pitch | 76854.3 sq ft | 7140 m² |
| One hectare | 107639 sq ft | 10000 m² |
| Central Park, New York | 36704935 sq ft | 3410000 m² |
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 metre is the SI unit of area, written m². It is the area of a square whose sides each measure one metre, and because the metre is a base unit, every other area unit in the system is derived from it by squaring a length. It is the unit in which most of the world buys homes, specifies materials and describes land.
Property is its largest everyday use. Outside the United States and, in part, the United Kingdom, dwellings are advertised, taxed and compared by their floor area in square metres, and price per square metre is the standard way of comparing one district with another. A modest one-bedroom flat runs to about 45 square metres, a family house between 100 and 150, and a single parking space takes up roughly 12.5.
Materials are sold and specified by the square metre because coverage, not volume, is what a builder needs to know. A litre of emulsion paint covers about ten square metres, floor tiles and laminate are priced by the square metre, and insulation is rated by its thermal resistance per square metre. Paper carries its own version of the same idea: the weight of a sheet stock is given in grams per square metre, so 80 g/m² office paper and 300 g/m² card are compared on one scale.
Physics uses the square metre as the denominator of almost every flux. Solar irradiance at the earth's surface peaks near 1000 watts per square metre, which is the figure solar panels are rated against. Pressure is force per square metre, and one newton per square metre is one pascal by definition. Heat loss through a wall is quoted in watts per square metre per kelvin, and sound intensity in watts per square metre.
Medicine uses it for the human body. An adult's skin covers between 1.6 and 2.0 square metres, and that figure is calculated for each patient before chemotherapy, because many drug doses are prescribed in milligrams per square metre rather than per kilogram. Burn severity is assessed as the percentage of body surface affected, using the same underlying measurement.
Where imperial units survive, the square foot competes directly with it. American and British commercial property is still let by the square foot, and one square metre is 10.76 square feet, which is why converted figures rarely come out round. Land at a larger scale moves to the hectare, equal to 10,000 square metres, and then to the square kilometre.
One square metre equals 10,000 square centimetres, about 10.764 square feet, about 1.196 square yards, or 0.0001 hectares.