Convert Square inches to square millimeters

1 square inch = 645.16 square millimeters · mm² = in² × 645.16

in²
Square millimeters
645.16mm²

1 square inch = 645.16 square millimeters

When you need this conversion

This conversion goes from square inches, used for small US area measurements, to square millimeters, used for wire gauge and small cross-sections. Both measure the same physical quantity, so the conversion is exact — the difference is which unit your source, tool, or region happens to use.

Square inches to square millimeters conversion table

Conversion table from square inches to square millimeters
Square inches (in²)Square millimeters (mm²)
1 in²645.16 mm²
2 in²1,290.32 mm²
3 in²1,935.48 mm²
5 in²3,225.8 mm²
10 in²6,451.6 mm²
15 in²9,677.4 mm²
20 in²12,903.2 mm²
25 in²16,129 mm²
50 in²32,258 mm²
75 in²48,387 mm²
100 in²64,516 mm²
250 in²161,290 mm²
500 in²322,580 mm²
1,000 in²645,160 mm²

The formula

mm² = in² × 645.16

Because both units measure area, the conversion is a single multiplication by a fixed factor. That factor never changes, so the result is exact.

Convert the other way

Square millimeters to square inches →

Related area conversions

All area conversions →

Frequently asked questions

How many square millimeters are in a square inch?
There are 645.16 square millimeters in 1 square inch. The formula is mm² = in² × 645.16.
How do you convert square inches to square millimeters?
Use the formula mm² = in² × 645.16. For example, 10 square inches equals 6,451.6 square millimeters.
Is the square inches to square millimeters conversion exact?
Yes. Square inches and square millimeters are both units of area, related by an exact defined factor. Displayed results are rounded for readability.
What is in² short for?
in² is the standard symbol for square inch. mm² is the symbol for square millimeter.