Convert Millimeters to Inches
Millimeters to inches is a common conversion in engineering, manufacturing, and hardware shopping, since parts and tools are often labeled in one unit but specified in the other. One millimeter is approximately 0.03937 inches.
Millimeters to Inches conversion table
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.03937 |
| 2 | 0.07874 |
| 3 | 0.11811 |
| 5 | 0.19685 |
| 10 | 0.393701 |
| 20 | 0.787402 |
| 50 | 1.968504 |
| 100 | 3.937008 |
| 500 | 19.685039 |
| 1,000 | 39.370079 |
The formula
To convert millimeters to inches, multiply the length in millimeters by 0.03937:
inches = millimeters × 0.03937
A worked example
Converting 100 mm into inches:
100 × 0.03937 = 3.937008 in
At smaller lengths, 10 mm comes to 0.393701 in, and 5 mm comes to 0.19685 in.
When you'll use it
Matching a metric bolt or drill bit size to an imperial equivalent, reading a phone or laptop's screen thickness spec, or converting a millimeter measurement from a technical drawing into inches for a US audience. This is one of the most frequently looked-up conversions in hardware and DIY contexts.
Frequently asked questions
How many inches are in a millimeter?
About 0.03937 inches. It's a rounded value — the exact figure has more decimal places, since a millimeter and an inch don't divide evenly.
Is the millimeter to inches conversion exact?
No, it's approximate. The reverse conversion (1 inch = 25.4 mm) is exact, but dividing 1 by 25.4 to go from millimeters to inches produces a repeating decimal, so 0.03937 is rounded for practical use.
What's a quick way to estimate millimeters to inches?
Divide by 25 as a rough shortcut. For anything that needs to be precise, like a bolt or screw size, use the full factor above.