Square inches

A square inch (in² or sq. in.) is a unit of measurement of area. 1 square inch is equal to the area of a square with sides that measure 1 inch:

A square area is a measurement made up of two lengths. Square units of area, such as square inches, are a result of multiplying two lengths. In the case of square inches, each length is measured in inches, so multiplying inches × inches results in inches². 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 in × 2 in rectangle is made up of 8 squares with an area of 1 in² each. The rectangle therefore has an area of 8 in²:

Systems of measurement

In the US customary system of units, square inches, square feet, square yards, square miles, and acres are some of the primary measurements of area. Square inches, feet, and yards are used for small to medium measurements of area, while square miles and acres are used for larger areas. For example, square inches may be used to measure the area of a piece of paper, cardboard, or poster, though usually these are described based on their length dimensions rather than their areas. Square inches would not be used to measure large tracts of land however. Instead square miles or acres may be used instead.

The standard unit of area in the International System of Units (SI) is the square meter (or metre). SI makes use of prefixes that denote the specific power of 10 that modifies a base unit (in this case the meter). For example the "centi-" prefix indicates 10^-2, so 1 meter is equal to 100 centimeters, making 1 m² = 10,000 cm². Converting between SI units is relatively straightforward because units are related by powers of 10.

Outside of the US, certain US customary units such as square feet may still be used, but for the most part, area is measured in square meters. As such, it is important to be able to convert between US customary and SI units of area since most countries around the world use SI, US customary units, or a mixture of SI and imperial (similar to US customary system) units of measurement.

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

144 square inches = 1 square foot

1296 square inches = 1 square yard

1550.003 square inches = 1 meter

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