Converters
Millimeters to Inches Converter
Convert millimeters to inches with the exact 25.4 factor. Enter a value for an instant result, then use the table for common small measurements.
Millimeters to Inches Converter
Enter a millimeter value to get the equivalent in inches.
Decimals and zero are supported. Results use four decimal places.
Common values (mm)
Result
3.937in
100 millimeters equals 3.937 inches.
Inches · shown to 4 decimal places, trailing zeros removed
Formula: inches = millimeters ÷ 25.4
Formula
How to convert mm to inches
Divide the millimeter value by 25.4. The factor is exact because the inch is defined as 25.4 millimeters.
Millimeters and inches are both used for small measurements, but they belong to different systems. A millimeter is one thousandth of a meter. An inch is 25.4 millimeters exactly. To convert, divide by 25.4; for example, 100 mm ÷ 25.4 = 3.9370 inches.
This conversion is common in manufacturing, electronics, jewelry, and hobby work, where components may be specified in either unit. A part described as 25.4 mm is exactly 1 inch, but a part described as 25 mm is slightly smaller at 0.9843 inches.
Millimeters → inches
in = mm ÷ 25.4
Divide the millimeter value by 25.4 to get inches.
50 mm ÷ 25.4 = 1.9685 in
Inches → millimeters
mm = in × 25.4
Multiply the inch value by 25.4 to return to millimeters.
2 in × 25.4 = 50.8 mm
Watch the difference
25 mm
0.9843 in
25.4 mm
1.0000 in
Quick table
Millimeters to inches conversion table
Small measurements from 1 mm to 1,000 mm, including the exact 25.4 mm mark.
| Millimeters (mm) | Inches (in) |
|---|---|
| 1 | 0.0394 |
| 2 | 0.0787 |
| 3 | 0.1181 |
| 4 | 0.1575 |
| 5 | 0.1969 |
| 10 | 0.3937 |
| 15 | 0.5906 |
| 20 | 0.7874 |
| 25 | 0.9843 |
| 25.4 | 1 |
| 30 | 1.1811 |
| 40 | 1.5748 |
| 50 | 1.9685 |
| 75 | 2.9528 |
| 100 | 3.937 |
| 150 | 5.9055 |
| 200 | 7.874 |
| 250 | 9.8425 |
| 500 | 19.685 |
| 1,000 | 39.3701 |
Inch values are rounded to four decimal places. The exact factor is 1 in = 25.4 mm.
Precision
When a few thousandths matter
At the millimeter scale, rounding can matter. Displaying an inch value to four decimal places keeps the rounding error below 0.00005 inches, but the original measurement may already have a looser tolerance. Always start from the precision of the source measurement rather than assuming the converted value is more accurate.
For a larger metric conversion, the centimeter to inch converter works the same way. For a quick lookup across a broad range, use the centimeter to inch chart.
Answers
Frequently asked questions
Quick answers to the questions people ask most about this conversion.
Have another question? Contact CMtoIN.
How many inches are in 1 millimeter?
One millimeter equals 0.0394 inches when rounded to four decimal places. The exact value is 1 ÷ 25.4 inches.
How do you convert millimeters to inches?
Divide the millimeter value by 25.4, because one inch is exactly 25.4 millimeters. For example, 100 mm ÷ 25.4 = 3.9370 inches.
What is 100 mm in inches?
100 millimeters equals 3.9370 inches, or just under 4 inches. This is close to the 4-inch nominal size of many small parts, but not an exact match.
What is 25.4 mm in inches?
25.4 millimeters equals exactly 1 inch. This is the definition used for all millimeter-to-inch conversions.
Can I convert inches to millimeters here?
Yes. Use the swap button in the calculator to switch between millimeters and inches in either direction.
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