Square Mm to Square Inches Converter

How to convert square millimeters to square inches

Formulain² = mm² × 0.0015500031

Because one square inch equals 645.16 square millimeters, you can also divide: in² = mm² ÷ 645.16.

A square millimeter is smaller than a square inch: it takes 645.16 square millimeters to make one square inch.

Worked examples

1 square millimeter1 mm² × 0.0015500031 = 0.0015500031 in²
5 square millimeters5 mm² × 0.0015500031 = 0.0077500155 in²
10 square millimeters10 mm² × 0.0015500031 = 0.015500031 in²
20 square millimeters20 mm² × 0.0015500031 = 0.031000062 in²
100 square millimeters100 mm² × 0.0015500031 = 0.15500031 in²

Square millimeters to square inches conversion table

Values are calculated by the conversion engine and rounded to 8 significant figures.

Square millimeters to square inches: 0.1–10 mm²
Square millimeters (mm²)	Square inches (in²)
0.1 mm²	0.00015500031 in²
0.25 mm²	0.00038750078 in²
0.5 mm²	0.00077500155 in²
1 mm²	0.0015500031 in²
2 mm²	0.0031000062 in²
3 mm²	0.0046500093 in²
4 mm²	0.0062000124 in²
5 mm²	0.0077500155 in²
6 mm²	0.0093000186 in²
7 mm²	0.010850022 in²
8 mm²	0.012400025 in²
9 mm²	0.013950028 in²
10 mm²	0.015500031 in²

Square millimeters to square inches: 12–1,000 mm²
Square millimeters (mm²)	Square inches (in²)
12 mm²	0.018600037 in²
15 mm²	0.023250047 in²
20 mm²	0.031000062 in²
25 mm²	0.038750078 in²
30 mm²	0.046500093 in²
40 mm²	0.062000124 in²
50 mm²	0.077500155 in²
75 mm²	0.11625023 in²
100 mm²	0.15500031 in²
250 mm²	0.38750078 in²
500 mm²	0.77500155 in²
1,000 mm²	1.5500031 in²

About the units

Square millimeter (mm²)

Used for wire cross-sections in metric countries (e.g. 2.5 mm² cable). One square millimeter equals 0.000001 square meters (m²).

Square inch (in²)

The square inch (in²) is a unit of area in the US customary system. One square inch equals 0.00064516 square meters (m²).

Frequently asked questions

How many square inches are in one square millimeter?

There are 0.0015500031 square inches in one square millimeter, and this value is exact by definition.

How do I convert square millimeters to square inches?

Multiply the number of square millimeters by 0.0015500031. For example, 10 mm² × 0.0015500031 = 0.015500031 in².

How many square millimeters are in one square inch?

One square inch equals 645.16 square millimeters. That is the reverse factor, 1 ÷ 0.0015500031.

What is 10 square millimeters in square inches?

10 mm² = 0.015500031 in².

Is this mm² to in² converter accurate?

Yes. Both units are defined exactly in terms of SI units, so the conversion factor is exact; results are shown to 12 significant figures by default and you can change precision in the converter. Calculations run in your browser using the same tested engine that generated this page.