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Inches to millimeters

1 inch = 25.4 millimeters

Type a value in inches (in) to get millimeters (mm) straight away. An inch is larger than a millimeter, so the number goes up. Both units belong to length, measured here against the meter.

1 in = 25.4 mm

Formula

mm = in × 25.4

One inch is 25.4 millimeters, so multiply the inch value by that factor. Here in is the value in inches and mm is the result in millimeters.

Worked example: 12 inches × 25.4 = 304.8 millimeters.

Inches to millimeters table

inches (in)millimeters (mm)
1 in25.4 mm
2 in50.8 mm
3 in76.2 mm
4 in101.6 mm
5 in127 mm
6 in152.4 mm
7 in177.8 mm
8 in203.2 mm
9 in228.6 mm
10 in254 mm
15 in381 mm
20 in508 mm
25 in635 mm
30 in762 mm
40 in1,016 mm
50 in1,270 mm
60 in1,524 mm
75 in1,905 mm
100 in2,540 mm

Everyday inches in millimeters

What it isinmm
a thumb width (about)1 in25.4 mm
a common phone screen diagonal6.1 in154.94 mm
a common laptop screen15.6 in396.24 mm
a 32-inch waist32 in812.8 mm
a 55-inch TV diagonal55 in1,397 mm

Quick estimate in your head

Multiply by about 25. For 12 in that gives 300 mm against an exact 304.8 mm, an error of 1.6%.

About the units

Inch (in). Exactly 2.54 cm since the 1959 international yard agreement. Common for screens, tyres and pipes.

Millimeter (mm). One thousandth of a meter. Used for engineering drawings, rainfall and screen sizes in some countries.

Going the other way, 1 millimeter is 0.0393701 inches.

Questions

How many millimeters are in 1 inch?

1 inch is 25.4 millimeters, and 1 millimeter is 0.0393701 inches.

How do I convert inches to millimeters?

Use mm = in × 25.4. For example, 12 inches × 25.4 = 304.8 millimeters.

Is the inch to millimeter factor exact?

The factor comes from the unit definitions. Results here are rounded to 6 significant digits for display.

How much is a 55-inch TV diagonal in millimeters?

55 in is 1,397 mm.

Source for the conversion factor: NIST SP 811, Appendix B (conversion factors).

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