About this converter
The inch (in) is an imperial and US customary length unit, and the millimeter (mm) is an SI metric length unit. One inch equals exactly 25.4 millimeters, so inch-to-millimeter conversion is exact rather than estimated.
This converter also supports foot, centimeter, and meter values for mixed drawings and product specifications. Machinists, mechanical engineers, product designers, and hardware buyers use inch and millimeter conversion when tolerances, fasteners, screens, pipes, and imported parts list dimensions in different systems.
How to Use This Converter
- Enter the length value in the input field.
- Select inches, millimeters, feet, centimeters, or meters as the source unit.
- Select the target unit for the converted result.
- Read the result and formula line below the input controls.
- Use Swap to reverse inches and millimeters without retyping the value.
Units Covered
| Unit | Symbol | Common Use |
|---|---|---|
| Inch | in | US hardware, screen sizes, machining drawings, and product dimensions. |
| Millimeter | mm | Metric engineering drawings, tolerances, fasteners, and small parts. |
| Foot | ft | Building dimensions, room layouts, and longer imperial measurements. |
| Centimeter | cm | School measurements, body dimensions, and consumer product sizes. |
| Meter | m | SI length reference for construction, lab work, and larger measurements. |
Inches to Millimeters Conversion Table
| From | To |
|---|---|
| 0.125 in | 3.175 mm |
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 0.75 in | 19.05 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 6 in | 152.4 mm |
| 10 in | 254 mm |
| 12 in | 304.8 mm |
How to Convert Inches to Millimeters
Inches to millimeters
For example, 2.5 in x 25.4 = 63.5 mm.
Millimeters to inches
For example, 80 mm / 25.4 = 3.14961 in.
When You Need to Convert Inches to Millimeters
A machinist reading a 0.375 in hole size may need the metric equivalent, 9.525 mm, before selecting a drill bit or checking a CAD model. Because 1 inch is exactly 25.4 mm, this conversion is stable for tolerance-sensitive work.
Product teams often receive supplier drawings in millimeters while packaging, retail listings, or US customer requirements use inches. A 6 in part is 152.4 mm, which matters when clearances, case dimensions, or shipping cartons are specified in metric units.
Home DIYers and technicians also meet mixed units in tools, fasteners, plumbing, and electronics. Converting 0.25 in to 6.35 mm makes it easier to compare imperial measurements with metric calipers and replacement parts.