Square Millimeter to Square Inch Converter

Area Converter

20 units available

Decimals:

From

To

0.00155

1 mm² = 0.00155 in²

Formula:

in² = mm² × 0.0015500031

With your value: 1 mm² = 0.00155 in²

How big is that?

Everyday references on a logarithmic scale, all expressed in square millimeter so you can sanity-check the result.

Your value1.00 mm²

Postage stamp (6.0e+2× your value)600 mm²

A4 sheet (6.3e+4× your value)6.25e+4 mm²

Parking space (1.3e+7× your value)1.25e+7 mm²

Tennis court (2.6e+8× your value)2.61e+8 mm²

Football pitch (7.1e+9× your value)7.14e+9 mm²

Other Square Millimeter to Square Inch conversions

2 mm² to in² 3 mm² to in² 4 mm² to in² 5 mm² to in² 6 mm² to in² 7 mm² to in² 8 mm² to in²

Square Millimeter to Square Inch Conversion Table

Square Millimeter (mm²)	Square Inch (in²)
0.5	0.000775
1	0.00155
2	0.0031
5	0.00775
10	0.0155
15	0.02325
20	0.031
25	0.03875
50	0.0775
100	0.155
250	0.387501
500	0.775002
1000	1.550003

Square Inch to Square Millimeter Conversion Table

Square Inch (in²)	Square Millimeter (mm²)
0.5	322.58
1	645.16
2	1,290.32
5	3,225.8
10	6,451.6
15	9,677.4
20	12,903.2
25	16,129
50	32,258
100	64,516
250	161,290
500	322,580
1000	645,160

Where these values come from

Every factor on this page is traced to the document that defines it. See the full provenance dataset or our methodology.

Square Millimeter (mm²)

Area

Exact conversion

Derived from the square metre via the length definitions above.

Source: NIST Special Publication 811, Guide for the Use of the International System of Units

National Institute of Standards and Technology (US) · Reviewed 2026-07-01

Square Inch (in²)

Area

Exact conversion

Derived from the square metre via the length definitions above.

Source: NIST Special Publication 811, Guide for the Use of the International System of Units

National Institute of Standards and Technology (US) · Reviewed 2026-07-01

How to Convert Square Millimeter to Square Inch

To convert from Square Millimeter (mm²) to Square Inch (in²), multiply the value by 0.0015500031.

Formula: in² = mm² × 0.0015500031

Reverse: mm² = in² × 645.16

Step-by-Step Example

Start with your value in Square Millimeter. For example: 5 mm²
Multiply by the conversion factor: 5 x 0.0015500031
The result is: 0.00775 in²

About Square Millimeter

The square millimeter (mm²) is a unit of area. One square millimeter equals 1.000000 × 10^-6 square metres. UnitConvertLab converts it against every other area unit using this exact definition, so results are reproducible to full double precision rather than rounded lookup tables.

Common uses: area calculations, engineering and science, education.

About Square Inch

The square inch (in²) is a unit of area. One square inch equals 0.00064516 square metres. UnitConvertLab converts it against every other area unit using this exact definition, so results are reproducible to full double precision rather than rounded lookup tables.

Common uses: area calculations, engineering and science, education.

Frequently Asked Questions

How many Square Inch are in 1 Square Millimeter?

There are exactly 0.0015500031 Square Inch in 1 Square Millimeter. This means the conversion factor from Square Millimeter to Square Inch is 0.0015500031.

What is the formula to convert Square Millimeter to Square Inch?

The formula to convert Square Millimeter to Square Inch is: in² = mm² × 0.0015500031. For example, to convert 10 Square Millimeter to Square Inch, you would multiply 10 by 0.0015500031.

What is a Square Millimeter?