MM to Inches Converter

Convert millimeters to inches instantly, with a reference table for common hardware and screen sizes.

Millimeters

Inches

1 mm = 0.0394 in

Multiply millimeters by 0.03937008 to get inches.

Millimeters to inches reference table

The conversions people look up most often, rounded to 4 decimal places.

Common millimeters to inches conversions
Millimeter (mm)	Inch (in)
1 mm	0.0394 in
2 mm	0.0787 in
3 mm	0.1181 in
5 mm	0.1969 in
10 mm	0.3937 in
12 mm	0.4724 in
15 mm	0.5906 in
20 mm	0.7874 in
25 mm	0.9843 in
50 mm	1.9685 in
100 mm	3.937 in
200 mm	7.874 in
300 mm	11.811 in

How the mm to inches converter calculation works

There are exactly 25.4 millimeters in an inch, so:

inches = millimeters ÷ 25.4

Millimeters are the working unit for anything precise — hardware, machining, phone screens, sheet material — which is why this conversion tends to matter more at the fine end than the coarse one. Getting four decimal places right is often the point.

A worked example: a 10 mm bolt is 10 ÷ 25.4 = 0.3937 inches. That is very close to, but not the same as, the 3/8" (0.375") imperial size — a 5.5% difference, and enough that the two are not interchangeable in a threaded hole. This is the classic reason metric and imperial hardware should not be mixed.

Two things worth keeping in mind:

Fractional inches need a second step. Shops usually want sixteenths or thirty-seconds, not decimals. Multiply the decimal by 16: 0.3937 × 16 = 6.3, so 10 mm is roughly 6/16" (3/8"), slightly over.
A millimeter is about 1/25th of an inch. Dividing by 25 instead of 25.4 gets you within 1.6% — good enough to eyeball a drill bit, not good enough to cut to.

Reverse the conversion by multiplying inches by 25.4, or tap the swap control on the converter above.

Frequently asked questions

How do I convert millimeters to inches?

Multiply the number of millimeters by 0.0393700787 to get inches.

How many inches are in 10 mm?

10 mm equals 0.3937 in. The reference table on this page lists the other values people look up most often.

How do I convert inches back to millimeters?

Divide the number of inches by 0.0393700787, or use the swap control on the converter above.

Is this conversion exact?

Yes. The factor is fixed by international definition rather than measured, so the conversion is exact - only the displayed rounding limits precision.

MM to Inches Converter