Square inches (in²) to Square millimeters (mm²) Conversion
Square inches
The square inch is a unit of area equal to exactly 6.4516 cm² (the square of 2.54 cm). It is used in engineering for specifying material cross-sections, pressure calculations (pounds per square inch = psi), and the dimensions of small components. Tile and flooring materials in the United States are sometimes measured in square inches for small-format tiles.
Square millimeters
The square millimetre is a unit of area equal to one millionth of a square metre (10⁻⁶ m²). In engineering, cross-sectional areas of wires and cables are standardised in square millimetres — electrical cable ratings specify conductor cross-sections in mm² (e.g., 1.5 mm², 2.5 mm², 4 mm²). In materials testing, stress is calculated as force per unit area in megapascals, where the area is expressed in square millimetres.
| Square inches (in²) | Square millimeters (mm²) |
|---|---|
| 0.1 in² | 64.516 mm² |
| 1 in² | 645.16 mm² |
| 2 in² | 1,290.32 mm² |
| 3 in² | 1,935.48 mm² |
| 5 in² | 3,225.80 mm² |
| 10 in² | 6,451.60 mm² |
| 20 in² | 12,903.20 mm² |
| 30 in² | 19,354.80 mm² |
| 50 in² | 32,258.00 mm² |
| 100 in² | 64,516.00 mm² |
| 1000 in² | 645,160.00 mm² |
Frequently Asked Questions (FAQ)
How many square millimeters are in 1 square inches?
1 square inches (in²) is exactly 645.160 square millimeters (mm²).
How do I convert square inches to square millimeters?
Multiply the value in square inches by 645.160 to get the result in square millimeters. Or use the converter above — type any number and see the result instantly.