Convert inches to millimeters (mm) and mm to inches instantly. Each inch equivalent to 25.4 mm — for engineering, 3D printing, woodworking, and metric ↔ imperial projects in the USA, UK, and Canada.
Live conversion as you type. 1 in × 25.4 = 25.4 mm (exact international inch)
Common inch values with mm and cm. Click a row to load the converter.
| Inches (in) | Millimeters (mm) | Centimeters (cm) | Notes |
|---|
Standard US fractional inch sizes used in woodworking, pipes, and wrenches.
| Fraction | Decimal (in) | Millimeters (mm) |
|---|
Screens, paper, bolts, and common objects — useful for USA, UK & Canada.
| Item | Inches | Millimeters |
|---|
Enter inch or mm values — one per line or comma-separated.
From inches or millimeters to cm, feet, yards, and meters.
NIST international inch — exact factors used by this calculator.
The international inch is defined as exactly 25.4 millimeters (since 1959, NIST standard). To convert inches to mm, multiply by 25.4: 2 in × 25.4 = 50.8 mm. To convert millimeters to inches, divide by 25.4: 50.8 mm ÷ 25.4 = 2 in.
In the United States, blueprints, lumber, and screen sizes often use inches while metric tools read millimeters. The UK and Canada officially use metric, but imperial inches still appear on imports, fasteners, and DIY guides. This converter bridges both systems for machining tolerances, 3D printer settings, and tape-measure readings.
| Inches | Millimeters | Common use |
|---|---|---|
| ⅛ in (0.125) | 3.175 mm | Small drill bit |
| ¼ in (0.25) | 6.35 mm | Hardware, fittings |
| ½ in (0.5) | 12.7 mm | Pipes, lumber thickness |
| 1 in | 25.4 mm | Base inch unit |
| 6 in | 152.4 mm | Phone / tablet screen |
| 12 in | 304.8 mm | One foot |
| 36 in | 914.4 mm | One yard |
1 inch is equivalent to 25.4 millimeters. This is the international standard inch definition.
You have to multiply 2 in and 25.4. And the result is 50.8 mm. Multiply any inch value by 25.4 for millimeters.
100 mm ÷ 25.4 ≈ 3.937 in. Use the swap button on this page for instant reverse conversion.
¼ inch = 6.35 mm (0.25 × 25.4). See the Fractions tab for more standard sizes.
Yes. Since 1959, 1 in = 25.4 mm by definition — not an approximation. Rounding only affects how many decimal places you display.
12 in × 25.4 = 304.8 mm — the same as one foot.
<!-- JavaScript for Conversion -->