MM to Inches Converter
Convert millimetres to inches instantly. Type a value below — the result updates as you type.
When you need to convert mm to inches
Millimetres-to-inches conversions turn up wherever fine precision matters: woodworking and joinery plans, 3D-printer settings, drill bits and fasteners, camera filter threads, jewellery sizes and rainfall figures. Hardware is the classic case — a metric M8 bolt is 8 mm (0.315 in) across, plywood sold as 18 mm is about 0.709 in (close to the imperial 3/4 in), and a 50 mm camera lens focuses at roughly a 2-inch focal length.
Because the ratio is fixed, you can scale any amount linearly — doubling the millimetres doubles the inches.
How to convert mm to inches
One inch is defined as exactly 25.4 millimetres — fixed by the 1959 international yard and pound agreement, so the factor itself introduces no rounding error. To convert, divide the number of millimetres by 25.4:
inches = millimetres ÷ 25.4
For example, 100 mm ÷ 25.4 = 3.937 inches. Equivalently, multiply by 0.03937 (which is 1 ÷ 25.4). The reverse is a multiplication: 6 in × 25.4 = 152.4 mm. For workshop fractions, remember 1/16 in ≈ 1.6 mm and 1/8 in ≈ 3.2 mm.
MM to inches conversion table
| Millimetres | Inches |
|---|---|
| 1 mm | 0.0394 in |
| 5 mm | 0.1969 in |
| 10 mm | 0.3937 in |
| 25 mm | 0.9843 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.9370 in |
| 300 mm | 11.811 in |
| 1000 mm | 39.370 in |
FAQ
How many inches are in a millimetre?
One millimetre = 0.03937 inches (1 ÷ 25.4). So 10 mm is 0.394 in and 25 mm is just under an inch at 0.984 in.
What is 18 mm in inches?
18 ÷ 25.4 = 0.7087 in — which is why 18 mm sheet material is treated as the metric stand-in for 3/4-inch stock.
How do I convert inches back to mm?
Multiply by 25.4. A 1/4-inch bit, for instance, is 0.25 × 25.4 = 6.35 mm. You can also use the inches to millimetres converter.
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