How to convert inches to millimetres
One inch is exactly 25.4 mm, so multiply inches by 25.4. Fractions are common in tools and DIY: 1/4" = 6.35 mm, 3/8" = 9.525 mm, 1/2" = 12.7 mm. Screen sizes are measured in inches diagonally, so a 27" monitor is about 686 mm corner to corner.
Inches to millimetres table
- 0.125 inches = 3.175 millimetres
- 0.25 inches = 6.35 millimetres
- 0.5 inches = 12.7 millimetres
- 0.75 inches = 19.05 millimetres
- 1 inches = 25.4 millimetres
- 2 inches = 50.8 millimetres
- 3 inches = 76.2 millimetres
- 6 inches = 152.4 millimetres
- 12 inches = 304.8 millimetres
- 24 inches = 609.6 millimetres
Frequently asked questions
How many mm in an inch?
Exactly 25.4 mm.
How do I convert millimetres back to inches?
Press "Swap units" and type your value. The same factor is applied in reverse.
Is the result exact?
Yes. Results use the exact defined factors and show up to 8 decimal places.
How to use the Inches to mm Converter
- Enter the value you want to convert.
- The result appears instantly as you type.
- Use the quick reference table below for common values.
- Copy the answer or reverse the conversion.
Why use this Inches to mm Converter
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Nothing you enter is uploaded or stored.
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Updates as you type, no waiting.
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Works on phones, tablets and desktops.
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Explained
Formulas, tables and sources on the page.
Inches to mm Converter: chart and reference data
Source: exact
UK DIY and engineering mix metric and imperial: copper pipe is metric (15 mm, 22 mm) but many screws, TVs and wheels are still described in inches.
| in | mm |
|---|---|
| 0 | 0 |
| 0.25 | 6.35 |
| 0.5 | 12.7 |
| 1 | 25.4 |
| 2 | 50.8 |
| 3 | 76.2 |
| 4 | 101.6 |
| 6 | 152.4 |
| 8 | 203.2 |
| 12 | 304.8 |
Inches to mm Converter compared with the alternatives
| Method | Speed | Accuracy | Best for |
|---|---|---|---|
| This converter | Instant | Exact ratio | Everyday and precise work |
| Mental rule of thumb | Fast | Approximate | Rough estimates |
| Printed conversion chart | Slow | Limited to listed values | Offline reference |
Who uses it in the UK
- Cooking with US or old British recipes
- DIY and home improvement
- Travel, sport and fitness
- School science and maths homework
More questions
What is the formula to convert in to mm?
mm = in × 25.4. Exact.
How accurate is this converter?
It uses the exact defined ratio and JavaScript double-precision numbers, so results are accurate to well beyond the decimal places shown. Rounding only happens for display.
Can I convert mm back to in?
Yes. Reverse the formula, or type into the other box if the tool shows both directions.
Does it work offline?
Yes. Once the page has loaded, all the maths happens in your browser, so it keeps working without a connection.
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