1 mm = 0.03937 in
| Millimeter (mm) | Inch (in) |
|---|---|
| 0.5 | 0.0197 |
| 1 | 0.0394 |
| 2 | 0.0787 |
| 3 | 0.1181 |
| 4 | 0.1575 |
| 5 | 0.1969 |
| 6 | 0.2362 |
| 8 | 0.315 |
| 10 | 0.3937 |
| 12 | 0.4724 |
| 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 |
To convert millimeters to inches, divide the number of millimeters by 25.4. There are exactly 25.4 millimeters in one inch.
1 mm = 0.03937 in
Convert 10 mm to inches: 10 ÷ 25.4 = 0.3937 inches
Convert 8 mm (camera lens focal point) to inches: 8 ÷ 25.4 = 0.315 inches
To convert inches to millimeters, multiply the inches by 25.4.
\u2022 1 mm is about the thickness of a credit card or a dime.
\u2022 5 mm (0.197 inches) is roughly the diameter of a pencil lead (mechanical pencil).
\u2022 10 mm (0.394 inches) is about the width of a AAA battery.
\u2022 25.4 mm is exactly 1 inch — the width of a US quarter coin.
Millimeter-to-inch conversion is critical for engineering, 3D printing, machining, and precision manufacturing. While millimeters are the global standard for precision measurements, many US-based specifications still use inches and fractions of inches.
The relationship is exact: 25.4 millimeters = 1 inch. This makes the conversion straightforward but the numbers often have many decimal places, which is why a converter tool is so useful.
Machinists, engineers, and manufacturers work in tight tolerances where even a fraction of a millimeter matters. Bolt sizes, drill bits, and pipe fittings come in both metric (M6, M8, M10) and imperial (1/4”, 3/8”, 1/2”) sizes. Knowing that an M6 bolt is about 0.236 inches helps when selecting the right tool or replacement part.
3D printers typically work in millimeters, but many designs from US-based makers specify dimensions in inches. Layer heights like 0.2 mm (0.008 inches) and nozzle diameters like 0.4 mm (0.016 inches) are standard specifications that benefit from accurate conversion.
Ring sizes, gemstone measurements, and jewelry wire gauges often use millimeters internationally and inches in the US. A 6mm wedding band is about 0.236 inches (just under 1/4 inch). A 1-carat round diamond is approximately 6.5 mm (0.256 inches) in diameter.
One millimeter equals approximately 0.03937 inches.
One inch equals exactly 25.4 millimeters.
Divide mm by 25.4 to get decimal inches, then find the nearest fraction. For example, 6 mm = 0.236 inches ≈ 15/64 inch.
10 mm equals approximately 0.3937 inches, or about 25/64 of an inch.
Neither is inherently more precise — precision depends on how many decimal places you use. However, millimeters are smaller units, so whole-number mm measurements are more precise than whole-number inch measurements.