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A square inch (plural: square inches) is a unit of area, equal to the area of a square with sides of one inch. The following symbols are used to denote square inches:

The square inch is a common unit of measurement in the United States and the United Kingdom. A common unit of pressure, pound per square inch (psi) is derived from this unit of area.

Equivalence with other units of area

1 square inch (assuming an international inch) is equal to: (the overbars indicate repeating decimals)