Drill Bit Size Chart
Number, letter, fractional, and metric drills, sorted by decimal inch size. Type a decimal to jump to the closest match.
Full chart
| Size | Decimal (in) | mm |
|---|
Why there are four different naming systems
Number drills (#80 through #1, smallest to largest) and letter drills (A through Z, continuing where numbers leave off) exist specifically to fill in the gaps between fractional sizes — a fractional-only index jumps in fairly coarse steps, while adding number and letter sizes gives a much finer selection for things like tap drills, where the exact 75%-engagement diameter rarely lands on a clean fraction. Metric drills are simply a separate, evenly-spaced set in millimeters that don't line up neatly with any of the inch-based sizes.
Verify before cutting anything critical
These decimal equivalents follow the standard ANSI B94.11M number, letter, and fractional drill sizes and standard metric drill sizes. Treat this as a fast reference for picking a close size, and cross-check the exact decimal against your own drill index or a manufacturer's chart before committing to a tolerance-critical hole — a transcribed reference chart is never a substitute for reading the actual drill's shank stamp.