Square inches to Square millimeters Converter

Square inches (in²). A square inch is 6.4516 square centimeters. It is used for small areas, and is the denominator in psi, the imperial pressure unit.

Square millimeters (mm²). A square millimeter is one millionth of a square meter. It is used for small cross-sections, circuit boards and material specifications.

Every factor is an exact definition, so the only loss is display rounding. Land figures quoted in acres and hectares are usually rounded at the source.

Area factors are the square of the corresponding length factors, so the numbers move much faster than a reader expects. A square meter contains 10,000 square centimeters, and a square kilometer a million square meters, not a thousand.

The units that share a name across systems are still different sizes: a square mile and a square kilometer differ by a factor of about 2.59, and an acre is a fixed area rather than a square with equal sides, so it does not convert like the length units it is named after.

Land is where the reciprocal matters most, because acres and hectares are both in use for the same plots. When a figure moves between them, check it against a shape you can picture — a hectare is a square 100 meters on each side — rather than against the number alone.