About This Millimeters to Inches Converter
The millimeter (mm) is the metric unit of choice for precision engineering — fastener diameters, PCB dimensions, drill bit sizes, and machined part tolerances are all specified in millimeters in international technical standards. The inch (in) remains the standard in US manufacturing, screen specifications, and hardware sold in North America. One inch equals exactly 25.4 millimeters, making the conversion precise rather than approximate.
This converter supports five length units: millimeters, inches, centimeters, meters, and feet. Machinists cross-referencing metric drawings against US tooling charts, electronics engineers comparing component datasheets from different continents, and hobbyists matching metric hardware to imperial drill sets all use this converter to prevent costly mis-cuts and wrong-part orders.
How to Use This Converter
- Enter your millimeter value in the Value field.
- Confirm Millimeter is selected in the From dropdown.
- Select Inch in the To dropdown (or any other target unit).
- The converted result and formula appear instantly.
- Use Swap to reverse between mm and inches without retyping.
Units Covered
| Unit | Symbol | Common Use |
|---|---|---|
| Millimeter | mm | Engineering drawings, fasteners, drill bits, PCB dimensions, small parts |
| Inch | in | US hardware, screen sizes, machining in North America |
| Centimeter | cm | Body measurements, clothing, furniture in metric countries |
| Meter | m | Structural dimensions, room lengths, SI base length unit |
| Foot | ft | Building heights, human height in US/UK, floor plans |
Millimeters to Inches Conversion Table
| Millimeters [mm] | Inches [in] |
|---|---|
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.11811 in |
| 5 mm | 0.19685 in |
| 6.35 mm | 0.25 in (¼ in) |
| 10 mm | 0.39370 in |
| 12.7 mm | 0.5 in (½ in) |
| 25.4 mm | 1 in |
| 50 mm | 1.9685 in |
| 100 mm | 3.9370 in |
| 200 mm | 7.8740 in |
| 300 mm | 11.811 in |
How to Convert Millimeters to Inches
To convert millimeters to inches, divide by 25.4:
Example: Convert 150 mm to inches:
To convert inches back to millimeters, multiply by 25.4:
Example: Convert 3 inches to millimeters:
When You Need to Convert Millimeters to Inches
Machinists and CNC operators work with technical drawings that can arrive in either unit system depending on the country of origin. A part specified as 6.35 mm is exactly 0.25 inches — a quarter-inch endmill fits precisely. Getting that conversion wrong by even 0.01 mm can push a tolerance out of spec on precision components where acceptable variation is ±0.05 mm.
Screen and display manufacturers express panel diagonals in inches for US marketing, but component specs and bezels are in millimeters. A 27-inch display measures 685.8 mm diagonally. Designing or specifying a custom enclosure, mount, or bracket for that panel requires the mm equivalent to work in CAD software using metric templates.
Woodworkers, plumbers, and hobbyists frequently encounter both systems when sourcing hardware. European pipe fittings are nominal in millimeters; US pipes are nominal in inches (and don't even correspond to actual diameter in millimeters cleanly). Converting 15 mm pipe to inches gives 0.5906 in — which is why 15 mm and ½-inch fittings are not interchangeable without an adapter.