Convert inches to millimeters for precision hardware and engineering.
Convert inches to millimeters using the official US customary standard conversion factor of 1 inch = 25.4 mm.
Convert inches to millimeters for precision hardware and engineering.
Convert inches to millimeters using the official US customary standard conversion factor of 1 inch = 25.4 mm.
Critical for machining, electronics, and precision engineering. Always use high precision for manufacturing and tool specifications. Approximate values only acceptable for general reference.
Common mistake: Confusing metric mm with US fractional inches. While 1 inch = 25.4 mm exactly, many DIY enthusiasts mistakenly use approximate values like 25 mm per inch, which causes significant errors in precision work.
| Item | Inches | Millimeters |
|---|---|---|
| Standard screw | 1/4 | 6.35 |
| Half inch | 1/2 | 12.7 |
| Drill bit #10 | 0.1935 | 4.915 |
| 1 inch bolt | 1 | 25.4 |
| Standard nail | 3.5 | 88.9 |
1 inch equals exactly 25.4 millimeters.
Millimeters are used for precision engineering, electronic components, and international manufacturing standards.
The official US customary standard defines 1 inch as exactly 25.4 millimeters.
For rough DIY work, 25 mm ≈ 1 inch may be acceptable, but for precision tasks like machining or electronics, always use the exact 25.4 mm.
Modern manufacturing uses metric standards globally. Converting US inches to millimeters ensures compatibility with international parts and machinery.
1/4 inch equals exactly 6.35 millimeters.
Last Updated: 2026 · Reviewed by the UnitFig editorial team