Convert mm to Inches
Convert millimeters to inches instantly — exact factors, common-value table, nothing uploaded.
Common conversions
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Millimeters to inches, where precision meets hardware
Most of the world manufactures in millimeters; US hardware, drill bits and fittings are specified in inches and fractions. The conversion is exact: 1 mm = 0.0393700787… in, because 25.4 mm is one inch by definition.
This page presets the converter to millimeters → inches, which is the direction you need when a metric spec has to match an imperial part. 10 mm is 0.3937 in, 20 mm is 0.7874 in, 100 mm is 3.937 in.
One caution: fractional inches are coarse. A 6 mm shaft is 0.236 in, which falls between 15/64 (0.234) and 1/4 (0.25) — the converter shows the decimal so you can pick the nearest real drill size deliberately.
Quick conversion table
Common values at a glance — computed locally with exact standard factors.
| Value (mm) | Converted (in) |
|---|---|
| 1 | 0.0393701 |
| 2 | 0.0787402 |
| 5 | 0.19685 |
| 10 | 0.393701 |
| 25 | 0.984252 |
| 50 | 1.9685 |
| 100 | 3.93701 |
How to convert mm to inches
Enter millimeters
Whole numbers or decimals both work; the answer appears as you type.
Read decimal inches
Decimal inches make it easy to compare against fractional sizes and tolerances.
Check the quick table
Common bolt and shaft sizes are listed below the converter for fast reference.
FAQs about this conversion
How many inches is 100 mm?
100 mm = 3.937 in — just under 4 inches, since 4 inches is 101.6 mm.
What mm value is exactly half an inch?
12.7 mm. Standard hardware sizes like 6 mm, 8 mm and 10 mm have no exact fractional-inch twin, which is why the decimal form matters.
Is a millimeter smaller than 1/16 inch?
Yes. 1/16 in = 1.5875 mm, so a millimeter is about two-thirds of a sixteenth.
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