Inches to MM Converter
Quick answer: To convert inches to MM, multiply by 25.4. For example, 10 in is 254 mm. One inch equals 25.4 mm.
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Use the Inches to MM Converter
Inches to MM formula and what each symbol means
mm = in × 25.4
| Symbol | Meaning |
|---|---|
| in | Inch |
| mm | Millimeter |
Inches to MM examples
1 in
1 in × 25.4 = 25.4 mm.
10 in
10 in × 25.4 = 254 mm.
100 in
100 in × 25.4 = 2,540 mm.
Inches compared with MM
One in is 25.4 times as large as one mm, so your number gets bigger when you convert inches to MM and smaller when you convert back. If the answer is not larger than what you typed, you divided instead of multiplying.
About inches and MM
Inch (in): The international inch, exactly 2.54 centimetres. Millimeter (mm): One thousandth of a metre.
Where inches to MM conversions are used
Road distances and maps use kilometres or miles, while building plans use metres, millimetres or feet. Screen sizes, tyres and clothing are usually given in inches, and body measurements in centimetres or inches.
How to calculate Inches to MM step by step
- Enter the value in in (the starting unit).
- Multiply by 25.4, because 1 in = 25.4 mm.
- The product is the value in mm. To go back, divide by 25.4 or multiply by 0.03937008.
Popular length conversions
How to read your Inches to MM result
Quick estimate: multiply by about 25 to get MM from inches; this is within 1.6% of the exact factor. Metric lengths convert by powers of ten, so you only move the decimal point.
| INCHES | MM |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 20 | 508 |
| 50 | 1,270 |
| 100 | 2,540 |
| 1,000 | 25,400 |
MM to Inches: quick table
| MM | INCHES |
|---|---|
| 1 | 0.03937008 |
| 5 | 0.1968504 |
| 10 | 0.3937008 |
| 25 | 0.984252 |
| 50 | 1.968504 |
| 100 | 3.937008 |
| 250 | 9.84252 |
| 500 | 19.68504 |
Common mistakes when calculating Inches to MM
- Mixing the international foot with the older US survey foot: the difference is about 2 parts per million and only matters in large land surveys.
- Dividing when you should multiply: from in to mm multiply by 25.4; from mm to in divide by 25.4.
Inches to MM FAQ
How many mm are in 1 in?
1 in equals 25.4 mm.
How many in are in 1 mm?
1 mm equals 0.03937008 in.
Is 1 in = 25.4 mm an exact conversion?
Yes. The inch and the millimeter are both defined exactly in SI terms, so the ratio has no measurement uncertainty; 25.4 is just that ratio shown to 7 significant figures.
What is an inch (in)?
The international inch, exactly 2.54 centimetres.
How can I estimate inches to MM in my head?
Quick estimate: multiply by about 25 to get MM from inches; this is within 1.6% of the exact factor.
What is 200 in in MM?
200 in = 5,080 mm (since 200 × 25.4).
What is 3 in in MM?
3 in = 76.2 mm (since 3 × 25.4).
What is 30 in in MM?
30 in = 762 mm (since 30 × 25.4).
How many decimals should I keep when converting in to mm?
Match the precision of your original measurement. For example, 254 mm rounds to 254 mm at 3 significant figures; keep more digits only for engineering or scientific work.
More in Length converters
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- Inches to KM Converter
- KM to Inches Converter
- Inches to Feet Converter
- KM to Meters Converter
- Inches to CM Converter
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Method, review and disclaimer
Edited by: Hemant Kumar and Anjita Rai, founders of ToolsVault (SEO and content professional, not a licensed adviser). Method: this tool runs in your browser using the formula shown on this page; the numbers you enter are not sent to our servers. Sources: NIST SP 811, Appendix B.8: conversion factors, BIPM: the SI base units