Length converter
Inches to Millimeters
Converting Inches to Millimeters is a single multiplication when you know the factor. One in equals 25.4 mm, so multiply the value in in by 25.4. The calculator below works in both directions and accepts decimals.
Formula 1 in = 25.4 mm
Need the other direction? Millimeters to Inches.
How to convert Inches to Millimeters
The inch is defined as exactly 2.54 centimetres, which anchors the whole imperial length system. The millimetre is one thousandth of a metre and is the usual unit for engineering tolerances.
To convert Inches to Millimeters, multiply the value in in by 25.4. For example, 10 in × 25.4 = 254 mm. This works because the ratio between the two units is constant for every value in length.
Worked examples
| in | mm |
|---|---|
| 1 in | 25.4 mm |
| 2.5 in | 63.5 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
Reverse conversion
| mm | in |
|---|---|
| 1 mm | 0.03937008 in |
| 5 mm | 0.19685039 in |
| 10 mm | 0.39370079 in |
| 25 mm | 0.98425197 in |
| 50 mm | 1.968504 in |
| 100 mm | 3.937008 in |
When this conversion is useful
This is the calculation you need when you are working across metric and imperial measurements, shopping abroad or reading a spec sheet. Because the factor is fixed, you can use the same number for a single measurement or for a batch: 1,000 in is 25,400 mm.
Is the conversion exact?
Yes for practical use: the factors come from international definitions, with rounding applied only for display.
Reference: BIPM SI Brochure and NIST SP 811. Last reviewed: 2026-11-01.
in to mm conversion chart
The chart lists the most requested values. For a value that is not here, use the converter at the top of the page.
| Inches (in) | Millimeters (mm) |
|---|---|
| 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 |
| 11 in | 279.4 mm |
| 12 in | 304.8 mm |
| 13 in | 330.2 mm |
| 14 in | 355.6 mm |
| 15 in | 381 mm |
| 16 in | 406.4 mm |
| 17 in | 431.8 mm |
| 18 in | 457.2 mm |
| 19 in | 482.6 mm |
| 20 in | 508 mm |
| 21 in | 533.4 mm |
| 22 in | 558.8 mm |
| 23 in | 584.2 mm |
| 24 in | 609.6 mm |
| 25 in | 635 mm |
| 26 in | 660.4 mm |
| 27 in | 685.8 mm |
| 28 in | 711.2 mm |
| 29 in | 736.6 mm |
| 30 in | 762 mm |
| 31 in | 787.4 mm |
| 32 in | 812.8 mm |
| 33 in | 838.2 mm |
| 34 in | 863.6 mm |
| 35 in | 889 mm |
| 36 in | 914.4 mm |
| 37 in | 939.8 mm |
| 38 in | 965.2 mm |
| 39 in | 990.6 mm |
| 40 in | 1,016 mm |
| 41 in | 1,041.4 mm |
| 42 in | 1,066.8 mm |
| 43 in | 1,092.2 mm |
| 44 in | 1,117.6 mm |
| 45 in | 1,143 mm |
| 46 in | 1,168.4 mm |
| 47 in | 1,193.8 mm |
| 48 in | 1,219.2 mm |
| 49 in | 1,244.6 mm |
| 50 in | 1,270 mm |
| 60 in | 1,524 mm |
| 70 in | 1,778 mm |
| 80 in | 2,032 mm |
| 90 in | 2,286 mm |
| 100 in | 2,540 mm |
Frequently asked questions
How many Millimeters are in 1 Inches?
1 in equals 25.4 mm.
How do I convert Inches to Millimeters?
Multiply the in value by 25.4. Example: 25 in = 635 mm.
What is 2.5 in in mm?
2.5 in = 63.5 mm.
Is the in to mm conversion exact?
Yes for practical use: the factors come from international definitions, with rounding applied only for display.
Does the calculator work offline?
Yes. The conversion runs in your browser with JavaScript, so it works after the page has loaded, even without a connection.