Millimeters to Inches Converter (mm to in)
1 in = 25.4 mm exactly. Convert millimeters to inches for wrenches, bolts, tires, batteries and paper sizes, with mm and inch charts.
in = mm ÷ 25.4
Millimeter (mm): The millimetre is one thousandth of a metre (0.001 m). There are 10 millimetres in a centimetre, and exactly 25.4 millimetres in an international inch.
Inch (in): The inch is exactly 2.54 centimetres, a value fixed by the 1959 international yard and pound agreement. It is used in the US and UK for screen sizes, tools, pipes and body measurements.
| Millimeter (mm) | Inch (in) |
|---|---|
| 1 | 0.0393700787402 |
| 5 | 0.196850393701 |
| 10 | 0.393700787402 |
| 25 | 0.984251968504 |
| 50 | 1.96850393701 |
| 100 | 3.93700787402 |
Metric sizes reach inch-based readers on wrench sets, bolts, drill bits, camera gear, tires and imported furniture. Since 1959 the inch has been exactly 25.4 mm, so dividing millimeters by 25.4 gives an exact inch figure; the only rounding is in how many decimals you choose to keep.
Workshop rulers in the US are marked in fractions rather than decimals, so the second chart starts at a sixteenth of an inch (0.0625) and steps through the fractions most tape measures show. A 10 mm wrench, for example, sits just above three-eighths of an inch, which is why the two sizes are not interchangeable.
How to use this tool
- Type a value in the Millimeter box to see it in inches, or type in the Inch box to convert the other way.
- Press ⇄ to swap the two units, or Load example for a typical value.
- Check the charts below for common values; for other units, open the Length converter.
Formula
in = mm ÷ 25.4
mm = in × 25.4
Both factors come from exact definitions: 1 inch = 25.4 millimeters and 1 millimeter = 0.0393700787402 inches (shown to 12 significant digits).
Example
Two conversions worked with the same factors the converter uses:
210 mm × 0.0393700787402 ≈ 8.26772 in
0.5 in × 25.4 = 12.7 mm
Millimeter to Inch chart
Common values from millimeters to inches, rounded to four decimal places.
| Millimeter (mm) | Inch (in) |
|---|---|
| 0.5 | 0.0197 |
| 1 | 0.0394 |
| 2 | 0.0787 |
| 3 | 0.1181 |
| 4 | 0.1575 |
| 5 | 0.1969 |
| 6 | 0.2362 |
| 8 | 0.315 |
| 10 | 0.3937 |
| 12 | 0.4724 |
| 13 | 0.5118 |
| 15 | 0.5906 |
| 17 | 0.6693 |
| 19 | 0.748 |
| 20 | 0.7874 |
| 22 | 0.8661 |
| 25 | 0.9843 |
| 30 | 1.1811 |
| 35 | 1.378 |
| 40 | 1.5748 |
| 45 | 1.7717 |
| 50 | 1.9685 |
| 75 | 2.9528 |
| 100 | 3.937 |
| 150 | 5.9055 |
| 200 | 7.874 |
| 300 | 11.811 |
Inch to Millimeter chart
The reverse direction for values people often look up.
| Inch (in) | Millimeter (mm) |
|---|---|
| 0.0625 | 1.5875 |
| 0.125 | 3.175 |
| 0.25 | 6.35 |
| 0.5 | 12.7 |
| 0.75 | 19.05 |
| 1 | 25.4 |
| 1.25 | 31.75 |
| 1.5 | 38.1 |
| 2 | 50.8 |
| 2.5 | 63.5 |
| 3 | 76.2 |
| 4 | 101.6 |
| 6 | 152.4 |
| 12 | 304.8 |
Metric sizes worth knowing in inches
| Item | Millimeter (mm) | Inch (in) |
|---|---|---|
| A4 paper, short side | 210 | 8.2677 |
| A4 paper, long side | 297 | 11.6929 |
| 35 mm film, width | 35 | 1.378 |
| AA battery, maximum length | 50.5 | 1.9882 |
| Bank card thickness (ISO/IEC 7810 ID-1) | 0.76 | 0.0299 |
| Tire width in a 225/45R17 size | 225 | 8.8583 |
| Headphone plug, standard mini jack | 3.5 | 0.1378 |
| Table tennis ball, diameter | 40 | 1.5748 |
Quick mental estimate
Divide the millimeters by 25, which is the same as multiplying by 4 and moving the decimal point two places: 100 mm → 4 in, against an exact 3.937 in. The shortcut uses 25 instead of 25.4, so it reads about 1.6% high.
Use the converter or the charts when the exact figure matters.
The two units
Millimeter (mm): The millimetre is one thousandth of a metre (0.001 m). There are 10 millimetres in a centimetre, and exactly 25.4 millimetres in an international inch.
Inch (in): The inch is exactly 2.54 centimetres, a value fixed by the 1959 international yard and pound agreement. It is used in the US and UK for screen sizes, tools, pipes and body measurements.
Frequently asked questions
What fraction of an inch is 1 mm?
About 0.03937 in, which lies between a thirty-second of an inch (0.03125) and three sixty-fourths (0.046875), slightly nearer the larger one. Five millimeters is close to 0.2 in, a handier figure to remember.
Can I use a 13 mm socket on a 1/2-inch bolt?
A 13 mm socket is about 0.512 in across, only 0.3 mm larger than half an inch (12.7 mm), so it often fits in a pinch. On a tight or rusted fastener the extra play can round off the corners, so use the matching size when you can.
How many inches is an A4 sheet?
A4 measures 210 × 297 mm, about 8.27 × 11.69 in. That is slightly narrower and longer than US Letter (8.5 × 11 in), so a page laid out for one size may need scaling to print on the other.
How precise is the result?
The converter uses the exact definitions above with browser floating-point arithmetic and shows up to 12 significant digits. The charts round to four decimal places for reading.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/millimeter-to-inch-converter/
Cite or embed this tool
kakaoCalc. (2026, November 8). Millimeters to Inches Converter (mm to in). https://kakao.mobile/tools/millimeter-to-inch-converter/
“Millimeters to Inches Converter (mm to in).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/millimeter-to-inch-converter/.
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