MM to Inches Converter
Convert millimeters to inches in one step. Enter a size in mm and get the exact value in inches, with the formula and a table of common values below.
Inches = Millimeters ÷ 25.4
MM to Inches Formula
One inch is exactly 25.4 millimeters, so to convert millimeters to inches you divide by 25.4. To convert inches back to millimeters, multiply by 25.4. The factor is exact, which makes this conversion reliable for engineering and manufacturing work.
How to Convert Millimeters to Inches
- Enter the size in millimeters. Decimals such as 6.35 are fine, and negative values are accepted where they make sense, such as tolerances or offsets.
- The result in inches updates instantly, or press Convert Now.
- Choose Swap Units to convert inches to millimeters, Copy Result to copy the value, or Clear to reset.
By hand: divide the millimeter value by 25.4. As a rough check, 25 mm is just under one inch.
Practical Examples
- Drill bit: a 6 mm bit is 0.23622 in, close to a ¼ inch (6.35 mm) bit.
- Film format: 35 mm film is 1.377953 in wide.
- Rainfall: 25.4 mm of rain is exactly 1 in, and 100 mm is 3.937008 in.
- Phone thickness: an 8 mm device is 0.314961 in thick.
- Pipe size: a 50 mm pipe is 1.968504 in across.
MM to Inches – Common Values
Quick reference for frequently used conversions
| Millimeters (mm) | Inches (in) | Centimeters (cm) |
|---|---|---|
| 1 mm | 0.03937 in | 0.1 cm |
| 2 mm | 0.07874 in | 0.2 cm |
| 3 mm | 0.11811 in | 0.3 cm |
| 5 mm | 0.19685 in | 0.5 cm |
| 6 mm | 0.23622 in | 0.6 cm |
| 8 mm | 0.314961 in | 0.8 cm |
| 10 mm | 0.393701 in | 1 cm |
| 12 mm | 0.472441 in | 1.2 cm |
| 15 mm | 0.590551 in | 1.5 cm |
| 20 mm | 0.787402 in | 2 cm |
| 25.4 mm | 1 in | 2.54 cm |
| 30 mm | 1.181102 in | 3 cm |
| 50 mm | 1.968504 in | 5 cm |
| 75 mm | 2.952756 in | 7.5 cm |
| 100 mm | 3.937008 in | 10 cm |
| 150 mm | 5.905512 in | 15 cm |
| 250 mm | 9.84252 in | 25 cm |
Where and Why This Conversion Is Used
Millimeters are the standard small-scale unit in metric engineering, while inches remain common in the US and in some trades worldwide. Converting accurately avoids parts that do not fit.
- Machining and manufacturing: drawings and tolerances may be metric while tooling is sold in inch sizes, or the reverse.
- Hardware and plumbing: bolts, drill bits, pipes and fittings are sized in mm or inches depending on the market.
- 3D printing and electronics: board dimensions, nozzle sizes and component spacing are often quoted in both.
- Photography: lens and film sizes use millimeters, while print and frame sizes use inches.
- Weather: rainfall and snowfall are reported in millimeters in most countries and inches in the US.
For larger lengths see the CM to Inches Converter or the Meters to Feet Converter.