A millimetre is one thousandth of a metre; one inch is exactly 25.4 millimetres, so the two units convert with the fixed factor 25.4.
Formula: inches = millimetres ÷ 25.4
Example: 100 mm ÷ 25.4 = 3.9370 in
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计算器: MM to Inches Converter.
使用计算器: MM to Inches Converter，根据输入获得清晰实用的结果。
此计算器尚未完全翻译——部分文本以英文显示。
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01
输入数值
输入时结果会更新。
02 / 答案
Direction
| Millimetres | Inches |
|---|---|
| 1 | 0.03937 |
| 2 | 0.07874 |
| 5 | 0.19685 |
| 10 | 0.393701 |
| 20 | 0.787402 |
| 25.4 | 1 |
| 50 | 1.968504 |
| 100 | 3.937008 |
| 500 | 19.685039 |
| 1000 | 39.370079 |
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Cite this calculator
Canonical URL: https://mathify.one/zh/conversion/mm-to-inches
Cite as: Mathify. (n.d.). 计算器: MM to Inches Converter. https://mathify.one/zh/conversion/mm-to-inches
Use Cases
Reading product dimensions
Convert a metric product listing into inches for US buyers.
Example: 300 mm becomes 11.8110 in
DIY and woodworking
Turn an inch measurement from a plan into millimetres before cutting.
Example: 2 in becomes 50.8 mm
Frequently Asked Questions
- How many millimetres are in an inch?
- Exactly 25.4 millimetres. This has been the international definition of the inch since 1959.
- How do I convert mm to inches?
- Divide the number of millimetres by 25.4. For example, 100 mm divided by 25.4 equals 3.9370 inches.
- What is 10 mm in inches?
- 10 mm is 0.3937 inches, which is a little more than three eighths of an inch.
Tips & Common Mistakes
Tips
- Keep 25.4 in mind: multiplying by it converts inches to millimetres, dividing converts millimetres to inches.
- For a fast estimate, divide millimetres by 25 and treat the result as slightly too large.
Common Mistakes to Avoid
- Multiplying by 25.4 when converting mm to inches; the correct operation is division.
- Rounding to 1 inch for values far below 25.4 mm and losing meaningful precision.
Last updated: September 11, 2026