Screw Size Converter
Convert between metric screw sizes (M2-M20), imperial sizes (#0-3/4 inch), and thread pitch.
Select a metric or imperial screw size to see its equivalents, or enter a custom diameter.
Screw sizes differ between metric and imperial systems.
Metric screws are labeled by diameter in mm (e.g., M6 = 6 mm). The standard coarse pitch is fixed per size.
Imperial screws use gauge numbers (#0–#14) or fractional inches. Thread count is in TPI (threads per inch).
Common metric to imperial equivalents:
| Metric | Diameter | Nearest Imperial | Diameter |
|---|---|---|---|
| M2 | 2.0 mm | #2 | 2.18 mm |
| M3 | 3.0 mm | #4 | 2.85 mm |
| M4 | 4.0 mm | #8 | 4.17 mm |
| M5 | 5.0 mm | #10 | 4.83 mm |
| M6 | 6.0 mm | 1/4" | 6.35 mm |
| M8 | 8.0 mm | 5/16" | 7.94 mm |
| M10 | 10.0 mm | 3/8" | 9.53 mm |
| M12 | 12.0 mm | 1/2" | 12.70 mm |
| M16 | 16.0 mm | 5/8" | 15.88 mm |
| M20 | 20.0 mm | 3/4" | 19.05 mm |
Thread pitch conversion:
- Pitch (mm) = 25.4 / TPI
- TPI = 25.4 / Pitch (mm)