Millimeters (mm) to Inches (in) Converter
Type a value in millimeters and instantly convert it to decimal inches and fractional inches.
How to convert millimeters to inches
Converting millimeters to inches is one of the most common metric to imperial conversions. The exact relationship is:
So to convert millimeters to inches, divide your millimeter value by 25.4. This is the same formula used by the calculator above.
Formula
inches = millimeters ÷ 25.4
Example: 50 mm ÷ 25.4 = 1.9685 inches (approximately)
Common millimeters to inches conversions
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 mm | 0.03937 in |
| 5 mm | 0.19685 in |
| 10 mm | 0.39370 in |
| 12 mm | 0.47244 in |
| 20 mm | 0.78740 in |
| 25.4 mm | 1.00000 in |
| 30 mm | 1.18110 in |
| 50 mm | 1.96850 in |
| 75 mm | 2.95276 in |
| 100 mm | 3.93701 in |
| 150 mm | 5.90551 in |
| 200 mm | 7.87402 in |
Why this conversion matters
You will often need mm to in conversion when you buy tools, compare screen sizes, work with 3D printing files, read engineering drawings, or follow DIY instructions from international sources. Many product dimensions are listed in both metric and imperial units, but not always in the format you need.
- Manufacturing: Bolt sizes, tolerances, and part dimensions.
- Construction: Sheet goods, drill bits, and hardware measurements.
- Electronics: Component spacing and enclosure dimensions.
- Daily life: Furniture, bike parts, and consumer products.
Rounding and precision tips
Depending on your project, you may need different levels of precision:
- 2 decimals (e.g., 1.97 in): quick estimates
- 3–4 decimals (e.g., 1.9685 in): design and light technical work
- Fractional inches (e.g., 1 31/32"): common for woodworking and tape measures
The calculator shows both decimal inches and a rounded fractional inch (to the nearest 1/16), so it is useful for both technical and practical measurements.
FAQ
How many millimeters are in one inch?
Exactly 25.4 millimeters.
How do I convert mm to inches quickly in my head?
A quick estimate is to divide by 25. For better accuracy, divide by 25.4. For example, 100 mm is roughly 4 inches, and exact is 3.937 in.
Can I use this for negative values?
Yes. Negative values can represent offsets or coordinate positions in CAD and machining contexts.
What is 300 mm in inches?
300 ÷ 25.4 = 11.811 inches.