Essential Conversion Reference
Whether you're following plans from different countries, using imported tools, or simply need to convert between fractional and metric measurements, this chart is your quick reference.
Common Conversions
1 inch = 25.4 mm 1 foot = 304.8 mm = 30.48 cm
Fractional Inches to Millimeters
| Fraction | Decimal (in) | Millimeters |
|---|---|---|
| 1/64 | 0.0156 | 0.397 |
| 1/32 | 0.0313 | 0.794 |
| 1/16 | 0.0625 | 1.588 |
| 3/32 | 0.0938 | 2.381 |
| 1/8 | 0.1250 | 3.175 |
| 5/32 | 0.1563 | 3.969 |
| 3/16 | 0.1875 | 4.763 |
| 7/32 | 0.2188 | 5.556 |
| 1/4 | 0.2500 | 6.350 |
| 5/16 | 0.3125 | 7.938 |
| 3/8 | 0.3750 | 9.525 |
| 7/16 | 0.4375 | 11.113 |
| 1/2 | 0.5000 | 12.700 |
| 9/16 | 0.5625 | 14.288 |
| 5/8 | 0.6250 | 15.875 |
| 11/16 | 0.6875 | 17.463 |
| 3/4 | 0.7500 | 19.050 |
| 13/16 | 0.8125 | 20.638 |
| 7/8 | 0.8750 | 22.225 |
| 15/16 | 0.9375 | 23.813 |
| 1 | 1.0000 | 25.400 |
Common Lumber Dimensions
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1x | 3/4" | 19mm |
| 2x | 1-1/2" | 38mm |
| 4/4 (1") | ~13/16" surfaced | ~21mm |
| 5/4 (1-1/4") | ~1-1/16" surfaced | ~27mm |
| 6/4 (1-1/2") | ~1-5/16" surfaced | ~33mm |
| 8/4 (2") | ~1-3/4" surfaced | ~44mm |
Metric Drill Bit Cross-Reference
When a plan calls for a metric drill bit and you only have fractional:
| Metric (mm) | Closest Fraction | Actual Size (mm) |
|---|---|---|
| 3mm | 1/8" | 3.175 |
| 4mm | 5/32" | 3.969 |
| 5mm | 13/64" | 5.159 |
| 6mm | 15/64" | 5.953 |
| 8mm | 5/16" | 7.938 |
| 10mm | 25/64" | 9.922 |
| 12mm | 15/32" | 11.906 |
Tips
- •Most woodworking tolerances are ±1/32" (0.8mm) or larger
- •For joinery, 0.5mm accuracy is usually sufficient
- •Digital calipers that display both imperial and metric are invaluable
