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Divide the number of millimeters by 25.4. One international inch equals exactly 25.4 mm.
Use a point or comma for decimals, without thousands separators (e.g. 1000.5).
Millimeters to inches
Divide the number of millimeters by 25.4. One international inch equals exactly 25.4 mm. The British spelling millimetres refers to the same unit. Unlike centimeters, millimeters use the divisor 25.4 rather than 2.54.
inches = millimeters ÷ 25.4 millimeters = inches × 25.4
| Millimeters (mm) | Decimal inches (in) |
|---|---|
| 1 | 0.03937 |
| 3 | 0.11811 |
| 5 | 0.19685 |
| 6 | 0.23622 |
| 6.35 | 0.25 |
| 9.525 | 0.375 |
| 10 | 0.3937 |
| 12.7 | 0.5 |
| 15 | 0.59055 |
| 20 | 0.7874 |
| 25.4 | 1 |
| 50 | 1.9685 |
| 100 | 3.93701 |
The converter returns decimal inches, not an automatically rounded fraction. A quarter inch (1/4) is 0.25 in and exactly 6.35 mm; three eighths (3/8) is 0.375 in and 9.525 mm. To convert a fraction, divide its numerator by its denominator, then multiply by 25.4 for millimeters. When choosing tools or parts, check tolerances: similar sizes are not always interchangeable.
12.7 ÷ 25.4 = 0.5 inches, or half an inch. A 6 mm panel is approximately 0.23622 inches, which is not exactly a quarter inch: 1/4 inch equals 6.35 mm.
A quarter inch is 6.35 mm, a half inch is 12.7 mm, three quarters is 19.05 mm and one inch is 25.4 mm.
This diagram shows the relationship, not physical size on your screen. Use a ruler to measure an object.
5 ÷ 25.4 ≈ 0.19685 inches. This is a decimal result rounded to five decimal places.
No. A quarter inch is exactly 6.35 mm, while 6 mm is approximately 0.23622 inches. The difference is 0.35 mm.
First divide 3 by 8 to get 0.375 inches. Multiply 0.375 by 25.4 to get exactly 9.525 mm. The converter displays decimal numbers rather than fractions.
Unit relationship reference: NIST — conversion factors. Long decimal values are rounded for display.
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