Convert millimetres to inches instantly
Type any measurement in millimetres and this converter gives you the exact inch value in real time. No rounding guesswork, no manual arithmetic – just a precise answer you can use straight away.
1 mm = 0.03937 inches. That single figure is the key to every mm-to-inch conversion, and the table below shows the most common values already worked out for you.
| Millimetres (mm) | Inches (in) |
|---|---|
| 1 mm | 0.0394 in |
| 2 mm | 0.0787 in |
| 5 mm | 0.1969 in |
| 10 mm | 0.3937 in |
| 25 mm | 0.9843 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.9370 in |
To go the other way – inches to mm – just flip the formula: multiply your inch value by 25.4.
How to use the mm to inches converter
- Make sure the From unit is set to mm and the To unit is set to inches.
- Type your millimetre value into the input box. The converted result appears immediately.
- Copy the inches value or keep typing to try different numbers.
- Need the reverse? Swap the units to convert inches back to millimetres.
Worked example – converting 25 mm to inches
Say you have a bolt that is 25 mm long and you need the inch equivalent.
- Start with the conversion factor: 1 mm = 0.03937 in
- Multiply: 25 × 0.03937 = 0.9843 inches
- That is just under 1 inch – close enough to a 1-inch bolt in imperial sizing.
Another common one: a phone screen border of 3 mm is 3 × 0.03937 = 0.118 inches – roughly ⅛ of an inch.
How the conversion is calculated
The formula is straightforward. One inch is defined as exactly 25.4 mm, so dividing by 25.4 always gives you inches:
inches = mm ÷ 25.4You can also multiply by the reciprocal:
inches = mm × 0.03937Both give the same answer. The ÷ 25.4 version is slightly more precise because 25.4 is the exact legal definition of an inch (set by international agreement in 1959 and used by the US NIST and the UK). The × 0.03937 version is a rounded shortcut – fine for everyday use.
Other ways people search for the same thing
People phrase this question in many different ways, but they all point to the same conversion:
- "mm to in" – the abbreviated form; same calculation.
- "millimeters to inches" – American English spelling (one l); identical result.
- "millimetres to inches" – British English spelling (two ls); same formula.
- "how many inches is X mm?" – divide X by 25.4.
- "convert mm to fractional inches" – divide by 25.4, then express as the nearest common fraction (e.g. ⅛, ¼, ½).
- "mm to decimal inches" – the plain decimal result this converter gives you.
If you need fractional inches for a woodworking or machining project, take the decimal result and match it to the nearest fraction: 0.5 in = ½ in, 0.25 in = ¼ in, 0.125 in = ⅛ in, and so on.
Quick tips and common mistakes
- Don't confuse cm and mm. A centimetre is 10 mm. If your ruler shows centimetres, multiply by 10 first, then convert. Or use our length converter with cm selected directly.
- Watch the decimal point. 10 mm is 0.394 in – not 3.94 in. A misplaced decimal is the most common error.
- Imperial fractions vs decimals. An American blueprint may show ⅜ in (0.375 in = 9.525 mm). This converter gives decimals; convert to fractions manually if needed.
- Precision matters in manufacturing. For engineering tolerances, keep at least 4 decimal places in inches (e.g. 0.0394 in, not 0.04 in).
- Phone screens and TVs are measured diagonally in inches, but bezels and components are usually spec'd in mm. This tool bridges that gap instantly.
Everything is calculated directly in your browser. No data is sent to any server, so your measurements stay completely private.
Bookmark this converter and reach for it the next time you hit a mm-to-inch roadblock – it handles any number from tiny PCB traces to large panels in one click.