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)

• 0.006 94 square feet (1 square foot is equal to 144 square inches)
• 0.000 771 604 9382 square yards (1 square yard is equal to 1,296 square inches)
• 6.4516 square centimetres (1 square centimetre is equal to 0.155 000 310... square inches)
• 0.000 645 16 square metres (1 square metre is equal to 1,550.003 100... square inches)