Inches to MM Converter
Convert inches to millimetres: 1 in = 25.4 mm. Exact factor, formula and a conversion chart.
Runs in your browser — nothing is uploadedConvert
Result
- 1 in
- 25.4 mm
- 1 mm
- 0.0393701 in
How it's calculated
millimetres = inches × 25.4
To convert in to mm, multiply by 25.4.
in in every unit
| millimetre | 25.4 mm |
| centimetre | 2.54 cm |
| metre | 0.0254 m |
| kilometre | 0.0000254 km |
| foot | 0.0833333 ft |
| yard | 0.0277778 yd |
| mile | 0.0000157828 mi |
| nautical mile | 0.0000137149 nmi |
in to mm conversion chart
| inch (in) | millimetre (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 |
| 12 in | 304.8 mm |
| 15 in | 381 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
How many millimetres are in 1 inch?
1 inch = 25.4 millimetres. To convert inches to millimetres, multiply by 25.4. For example, 10 in = 254 mm and 100 in = 2,540 mm. Enter any value above for an exact result.
The Unit Converter changes a value from one unit to another across 11 kinds of measurement: length, weight, temperature, volume, area, speed, time, digital storage, energy, pressure and fuel economy. It covers metric units (centimetres, kilograms, litres), US and UK imperial units (inches, pounds, gallons) and everyday ones such as cups, stones, acres and kilowatt-hours.
Conversions use the official definitions — 1 inch is exactly 2.54 cm, 1 pound exactly 0.45359237 kg, 1 US gallon exactly 3.785411784 litres — and the page shows the factor, the formula, the value in every other unit and a chart of common values, so you can check or reuse the numbers.
When to use it
- Converting height and weight between metric and imperial (cm ↔ feet and inches, kg ↔ lbs).
- Cooking with recipes from another country (cups, tablespoons, ml, grams, ounces).
- Reading weather and oven temperatures in Celsius or Fahrenheit.
- Property sizes in square feet, square metres, acres and hectares.
- File sizes (MB ↔ GB), fuel economy (mpg ↔ L/100 km) and tyre pressure (psi ↔ bar).
Tips for better results
- US and UK gallons and pints differ by about 20% — check which one a recipe or car manual uses.
- Temperature is not a simple multiplication: use the formula shown (°F = °C × 9/5 + 32).
- Storage makers use 1 GB = 1,000 MB, while some operating systems show GiB (1,024 MiB) — both are listed.
How to use the Unit Converter
- Choose the measurement, such as length or temperature.
- Enter the value and pick the units to convert from and to.
- Read the result, the value in every other unit and the conversion chart below.
Frequently asked questions
How do I convert inches to millimetres?
To convert inches to millimetres, multiply by 25.4. For example, 10 in = 254 mm.
How do I convert millimetres back to inches?
Press the swap button between the units. 1 mm = 0.0393701 in.
Is the conversion exact?
Yes. It uses the official definitions of the units; results are only rounded to six significant digits for display.
Are the conversions exact?
Yes. Units are converted with their defined factors — for example 1 inch is exactly 2.54 cm and 1 pound is exactly 0.45359237 kg — and results are rounded to six significant digits only for display.
Are cups and gallons US or UK?
Cups, pints, quarts and gallons are US customary units unless marked UK. UK (imperial) gallons and pints are listed separately because they are about 20% larger.
How many centimetres are in an inch?
Exactly 2.54 cm. To convert inches to centimetres, multiply by 2.54; to convert centimetres to inches, divide by 2.54.
How do I convert kilograms to pounds?
Multiply by 2.20462 (1 kg = 2.20462 lb). To convert pounds to kilograms, multiply by 0.453592.