How to convert inches to millimeters
To convert inches (in) to millimeters (mm), multiply the inch value by 25.4.
Millimeters = Inches × 25.4 Example: 0.5 inches × 25.4 = 12.7 mm Millimeters deliver fine-grained accuracy required for technical drafting and precision manufacturing. Because 1 inch is internationally defined as exactly 25.4 millimeters, multiplying by 25.4 guarantees zero calculation drift.
Fractional inch to millimeter reference table
Standard fractional inches used in hardware, drill bits, fasteners, and lumber converted directly to decimal millimeters:
| Fractional Inch | Decimal Inch | Millimeters (mm) | Common Application / Hardware Benchmark |
|---|---|---|---|
| 1/16 in | 0.0625 in | 1.5875 mm | Micro drill bit / precision shims |
| 1/8 in | 0.1250 in | 3.1750 mm | Standard 1/8" router shank / audio jack |
| 1/4 in | 0.2500 in | 6.3500 mm | Standard 1/4" audio jack / socket drive |
| 3/8 in | 0.3750 in | 9.5250 mm | Standard bolt size / plumbing fittings |
| 1/2 in | 0.5000 in | 12.7000 mm | Standard pipe diameter / copper tubing |
| 5/8 in | 0.6250 in | 15.8750 mm | Plywood thickness / arbor hole size |
| 3/4 in | 0.7500 in | 19.0500 mm | Standard nominal lumber thickness |
| 1 in | 1.0000 in | 25.4000 mm | 1 Imperial Inch benchmark |
| 2 in | 2.0000 in | 50.8000 mm | Standard hitch receiver width |
| 12 in | 12.0000 in | 304.8000 mm | 1 Foot / architectural scale ruler |
Working with centimeter scale design drawings? Try our Inches to CM Converter. To reverse millimeter values back to imperial, use our MM to Inches Converter.
Frequently asked questions
How many mm are in an inch?
There are exactly 25.4 millimeters in 1 inch.
How many mm is 2 inches?
2 inches equals exactly 50.8 millimeters (2 × 25.4 = 50.8 mm).
How do I convert millimeters back to inches?
Divide the millimeter value by 25.4, or use our dedicated MM to Inches Converter.
How many mm is 1/4 inch?
1/4 inch (0.25 in) equals exactly 6.35 millimeters.