Drill Bit Sizes (Number / Letter)
Numbered and lettered drill bit sizes as decimal inches and millimeters.
| Size | Decimal | Metric |
|---|---|---|
| 1 | 0.228 | 5.791 |
| 2 | 0.221 | 5.613 |
| 3 | 0.213 | 5.41 |
| 4 | 0.209 | 5.309 |
| 5 | 0.2055 | 5.22 |
| 6 | 0.204 | 5.182 |
| 7 | 0.201 | 5.105 |
| 8 | 0.199 | 5.054 |
| 9 | 0.196 | 4.978 |
| 10 | 0.1935 | 4.915 |
| 11 | 0.191 | 4.851 |
| 12 | 0.189 | 4.801 |
| 13 | 0.185 | 4.699 |
| 14 | 0.182 | 4.623 |
| 15 | 0.18 | 4.572 |
| 16 | 0.177 | 4.496 |
| 17 | 0.173 | 4.394 |
| 18 | 0.1695 | 4.305 |
| 19 | 0.166 | 4.216 |
| 20 | 0.161 | 4.089 |
| 21 | 0.159 | 4.039 |
| 22 | 0.157 | 3.988 |
| 23 | 0.154 | 3.912 |
| 24 | 0.152 | 3.861 |
| 25 | 0.1495 | 3.797 |
| 26 | 0.147 | 3.734 |
| 27 | 0.144 | 3.658 |
| 28 | 0.1405 | 3.569 |
| 29 | 0.136 | 3.454 |
| 30 | 0.1285 | 3.264 |
| A | 0.234 | 5.944 |
| B | 0.238 | 6.045 |
| C | 0.242 | 6.147 |
| D | 0.246 | 6.248 |
| E | 0.25 | 6.35 |
| F | 0.257 | 6.528 |
| G | 0.261 | 6.629 |
| H | 0.266 | 6.756 |
| I | 0.272 | 6.909 |
| J | 0.277 | 7.036 |
| K | 0.281 | 7.137 |
| L | 0.29 | 7.366 |
| M | 0.295 | 7.493 |
| N | 0.302 | 7.671 |
| O | 0.316 | 8.026 |
| P | 0.323 | 8.204 |
| Q | 0.332 | 8.433 |
| R | 0.339 | 8.611 |
| S | 0.348 | 8.839 |
| T | 0.358 | 9.093 |
| U | 0.368 | 9.347 |
| V | 0.377 | 9.576 |
| W | 0.386 | 9.804 |
| X | 0.397 | 10.084 |
| Y | 0.404 | 10.262 |
| Z | 0.413 | 10.49 |
About this lookup
- When to use number/letter bits?
- Mostly for tapping: tapping drill sizes that fall between fractional sizes.
- Tap drill size for 1/4-20?
- Use a #7 drill (0.201") — 75% thread is the standard.