Convert Inches to Millimeters
Convert units instantly — free, private, no signup.
Common Conversions
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.1 | 2.5400 |
| 0.25 | 6.3500 |
| 0.5 | 12.7000 |
| 1 | 25.4000 |
| 2 | 50.8000 |
| 3 | 76.2000 |
| 5 | 127.00 |
| 10 | 254.00 |
| 15 | 381.00 |
| 20 | 508.00 |
| 25 | 635.00 |
| 50 | 1270.00 |
| 75 | 1905.00 |
| 100 | 2540.00 |
| 150 | 3810.00 |
| 250 | 6350.00 |
| 500 | 12700.00 |
| 1000 | 25400.00 |
| 2500 | 63500.00 |
| 5000 | 127000.00 |
What Is Inches TO Millimeters?
One inch equals exactly 25.4 millimeters. This is perhaps the single most important length conversion in manufacturing, as countless engineering drawings, bolt specifications, and machine parts must be translated between imperial and metric systems. Standard drill bit sets come in both fractional-inch and millimeter sizes, and knowing that 1/4 inch is 6.35 mm or that 1/2 inch is 12.7 mm saves machinists time every day. The conversion is exact because the inch was internationally defined as 25.4 mm in 1959. Wrench sizes, pipe diameters, and sheet metal gauges all require this conversion when sourcing components internationally. Even in predominantly metric countries, certain industries like aviation and oil drilling still use inch-based specifications.
Formula
Multiply the inch value by 25.4 to get millimeters. This is an exact conversion factor by definition. For fractional inches, convert the fraction to decimal first: for example, 3/8 inch = 0.375 inches = 0.375 x 25.4 = 9.525 mm.
Best For:
- Manufacturing: converting bolt, screw, and fastener sizes between imperial and metric
- Machining: selecting metric drill bits to match imperial hole specifications
- Plumbing: converting pipe diameters from inches to millimeters for international fittings
- Aviation maintenance: imperial aircraft specifications needing metric tooling
- Screen and display measurements: converting pixel pitch and display thickness to mm
How to Inches TO Millimeters
Enter a Value
Type the number you want to convert in the input field above.
See Instant Result
The converted value is calculated instantly — no button click needed.
Swap or Explore
Click the swap button to reverse the conversion, or explore the common values table.
TweakFiles vs Google vs UnitConverters.net
| Feature | TweakFiles | UnitConverters.net | |
|---|---|---|---|
| Price | Free forever | Free | Free |
| File Privacy | 100% client-side | Server-side | Server-side |
| Dedicated page per pair | Yes — SEO optimized | No | Yes |
| Common values table | 20+ values | No | Limited |
| Formula explanation | Detailed | No | Brief |
| Ads | None | Minimal | Heavy |