Convert Square millimeters to square inches

1 square millimeter = 0.001550003 square inches · in² = mm² ÷ 645.16

mm²
Square inches
0.001550003in²

1 square millimeter = 0.001550003 square inches

When you need this conversion

This conversion goes from square millimeters, used for wire gauge and small cross-sections, to square inches, used for small US area measurements. 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 millimeters to square inches conversion table

Conversion table from square millimeters to square inches
Square millimeters (mm²)Square inches (in²)
1 mm²0.001550003 in²
2 mm²0.003100006 in²
3 mm²0.004650009 in²
5 mm²0.007750016 in²
10 mm²0.0155 in²
15 mm²0.02325 in²
20 mm²0.031 in²
25 mm²0.03875 in²
50 mm²0.0775 in²
75 mm²0.11625 in²
100 mm²0.155 in²
250 mm²0.387501 in²
500 mm²0.775002 in²
1,000 mm²1.55 in²

The formula

in² = mm² ÷ 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 inches to square millimeters →

Related area conversions

All area conversions →

Frequently asked questions

How many square inches are in a square millimeter?
There are 0.001550003 square inches in 1 square millimeter. The formula is in² = mm² ÷ 645.16.
How do you convert square millimeters to square inches?
Use the formula in² = mm² ÷ 645.16. For example, 10 square millimeters equals 0.0155 square inches.
Is the square millimeters to square inches conversion exact?
Yes. Square millimeters and square inches are both units of area, related by an exact defined factor. Displayed results are rounded for readability.
What is mm² short for?
mm² is the standard symbol for square millimeter. in² is the symbol for square inch.