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: square in sq inches, sq inch, sq in inches/-2, inch/-2, in/-2 inches^2, inch^2, in^2 inches2, inch2, in2 (also denoted by "2) historic engineering drawings □″ (number with a square & a double apostrophe, both as an exponent) 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) square feet (1 square foot is equal to 144 square inches) square yards (1 square yard is equal to 1,296 square inches) square centimetres (1 square centimetre is equal to square inches) square metres (1 square metre is equal to square inches) Units of area Imperial units Customary units of measurement in the United States ja:インチ#平方インチ