Square feet

A square foot (ft² or sq. ft.) is a unit of measurement of area. 1 square foot is equal to the area of a square with sides that measure 1 foot.

A square area is a measurement made up of two lengths. Square units of area, such as square feet, are a result of multiplying two lengths. In the case of square feet, each length is measured in feet, so multiplying feet × feet results in feet². The measured area does not need to be in the shape of a square; any area can be calculated, or estimated, as the area made up by some number of unit squares.

For example, a 4 ft × 2 ft rectangle is made up of 8 squares with an area of 1 ft² each. The rectangle therefore has an area of 8 ft²:

Systems of measurement

In the US customary system of units, inches, feet, and yards are some of the primary measurements of length. As such, the primary units of area in the US customary system are square inches, square feet, and square yards. These units are used for measuring smaller to medium sized areas. For example, property area (apartment, condominium, house, etc.) in the US is most commonly measured using square feet. For significantly larger measurements of area, the US also uses acres, or even square miles.

Outside of the US, most countries use the International System of Units (SI). The standard unit of length in SI is the meter (or metre), so the standard unit of area is square meters (m²). While some countries may use other measurements of area (including square feet, also usually for measuring property area), most use square meters. As such, it is important to be able to convert between US customary and SI units of area, the two most widely used systems of measurement around the world.

Below are the relationships between square feet and some other measurements of area.

1 square foot = 144 square inches

9 square feet = 1 square yard

43,560 square feet = 1 acre

10.764 square feet = 1 square meter

Note that these conversions are rounded to 3 decimal places, so they are not exact.

Note that for units in the US customary system, if you know the relationships between inches, feet, and yards, you can determine the relationships between square inches, square feet, and square yards by squaring the units. Since there are 12 inches in 1 foot, there are 144 inches in 1 square foot. Similarly, there are 3 feet in a yard, so there are 9 square feet in 1 square yard.