Inches to Millimeters Converter (inch to mm)

Enter a value in inches to see it in millimeters instantly, or type in the millimeters box to convert the other way. 1 inch = 25.4 millimeters, and 1 millimeter = 0.039370079 inches.

Multiply inches by 25.4. Fractional inches convert the same way: 3/8 in = 0.375 × 25.4 = 9.525 mm. Screen sizes, wrench sizes and drill bits are the usual reasons to convert.

From

1 inch = 25.4 millimeters. Formula: mm = in × 25.4 (or in ÷ 0.039370079)

1 inch in all length units

Millimeters (mm)	25.4
Centimeters (cm)	2.54
Meters (m)	0.0254
Kilometers (km)	0.0000254
Feet (ft)	0.083333333
Yards (yd)	0.027777778
Miles (mi)	0.0000157828
Nautical miles (nmi)	0.0000137149
Gaj (gaj)	0.027777778

How to convert inches to millimeters

mm = in × 25.4

Multiply the number of inches by 25.4. To convert millimeters back to inches, multiply by 0.039370079, or divide by 25.4.

Example: 5 inches × 25.4 = 127 millimeters.

Inches to Millimeters conversion table

Inches	Millimeters
1 in	25.4 mm
2 in	50.8 mm
3 in	76.2 mm
4 in	101.6 mm
5 in	127 mm
6 in	152.4 mm
7 in	177.8 mm
8 in	203.2 mm
9 in	228.6 mm
10 in	254 mm
12 in	304.8 mm
15 in	381 mm
20 in	508 mm
25 in	635 mm
30 in	762 mm
40 in	1,016 mm
50 in	1,270 mm
60 in	1,524 mm
70 in	1,778 mm
75 in	1,905 mm
80 in	2,032 mm
90 in	2,286 mm
100 in	2,540 mm
200 in	5,080 mm
250 in	6,350 mm
500 in	12,700 mm
1,000 in	25,400 mm

Millimeters	Inches
1 mm	0.039370079 in
2 mm	0.078740157 in
3 mm	0.11811024 in
4 mm	0.15748031 in
5 mm	0.19685039 in
6 mm	0.23622047 in
7 mm	0.27559055 in
8 mm	0.31496063 in
9 mm	0.35433071 in
10 mm	0.39370079 in
12 mm	0.47244094 in
15 mm	0.59055118 in
20 mm	0.78740157 in
25 mm	0.98425197 in
30 mm	1.1811024 in
40 mm	1.5748031 in
50 mm	1.9685039 in
60 mm	2.3622047 in
70 mm	2.7559055 in
75 mm	2.9527559 in
80 mm	3.1496063 in
90 mm	3.5433071 in
100 mm	3.9370079 in
200 mm	7.8740157 in
250 mm	9.8425197 in
500 mm	19.685039 in
1,000 mm	39.370079 in

About the inch and the millimeter

The inch is exactly 25.4 mm. It survives in screen sizes, tyre and wheel sizes, pipe diameters and paper sizes even in metric countries.

The millimeter (millimetre) is one thousandth of a meter. It is the working unit on engineering drawings, screw and bolt sizes, paper sizes, phone dimensions and rainfall reports.

Frequently asked questions

How many millimeters are in a inch?

There are 25.4 millimeters in 1 inch. For any number of inches, multiply by 25.4.

How many inches are in a millimeter?

1 millimeter = 0.039370079 inches. To convert millimeters to inches, multiply by 0.039370079 or divide by 25.4.

What is 5 inches in millimeters?

5 inches = 127 millimeters (5 × 25.4).

Is the inch to mm conversion exact?

Yes. The 1959 international yard and pound agreement defined the yard as exactly 0.9144 meters, which makes the inch exactly 25.4 mm, the foot exactly 0.3048 m and the mile exactly 1,609.344 m. Every factor on this page follows from those definitions, so it is exact rather than approximate. Results are rounded to eight significant digits for display.

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Last updated September 3, 2026. Formulas are shown on the page and checked against the worked example.

Conversion factors are exact international definitions where one exists and standard reference values elsewhere. Results are rounded to 8 significant digits.