CalcPairsMillimeters to Inches Converter (mm to in)
100 millimetres is 3.937008 inches. One inch is exactly 25.4 mm, so millimetres ÷ 25.4 gives inches — the conversion behind every metric bolt sold next to an imperial drill bit.
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How this conversion works
Millimetres are the language of engineering drawings, camera filters, jewellery and weather forecasts; inches still label drill bits, screws and screen sizes in the US. This converter runs both ways live, so a 6 mm bolt and a ¼-inch bit can be compared on the spot (6 mm = 0.23622 in — close to, but not exactly, a quarter inch).
The table below covers the sizes that actually come up, from 1 mm up to 100 mm in fine steps at the small end where a fraction of a millimetre matters.
The exact formula
inches = millimetres ÷ 25.4
1 inch = 25.4 mm exactly. The reverse is millimetres = inches × 25.4.
Millimeters to Inches conversion table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.03937 |
| 2 | 0.07874 |
| 3 | 0.11811 |
| 4 | 0.15748 |
| 5 | 0.19685 |
| 6 | 0.23622 |
| 7 | 0.275591 |
| 8 | 0.314961 |
| 9 | 0.354331 |
| 10 | 0.393701 |
| Millimeters (mm) | Inches (in) |
|---|---|
| 15 | 0.590551 |
| 20 | 0.787402 |
| 25 | 0.984252 |
| 30 | 1.181102 |
| 35 | 1.377953 |
| 40 | 1.574803 |
| 45 | 1.771654 |
| 50 | 1.968504 |
| 55 | 2.165354 |
| 60 | 2.362205 |
| Millimeters (mm) | Inches (in) |
|---|---|
| 65 | 2.559055 |
| 70 | 2.755906 |
| 75 | 2.952756 |
| 80 | 3.149606 |
| 85 | 3.346457 |
| 90 | 3.543307 |
| 95 | 3.740157 |
| 100 | 3.937008 |
Frequently asked questions
How many millimetres are in an inch?
Exactly 25.4 mm.
Is 6 mm the same as ¼ inch?
Not quite: ¼ inch is 6.35 mm. The 0.35 mm difference matters for bolts and bearings even though it looks tiny.
What is 1 mm in inches?
0.0393701 inches — about 1/25th of an inch, which is exactly what the definition says.