Letter drill size chart (A–Z)
Letter drills fill the gap above #1 (0.228 in): A is 0.234 in and Z is 0.413 in. Several are standard tap drills, such as F for 5/16-18 and I for 5/16-24. Click a size for its speeds and feeds.
| Drill | Inch | mm | Nearest other drills | Tap drill for |
|---|---|---|---|---|
| A | 0.2340 | 5.944 | 15/64" (0.2344) · 5.9 mm (0.2323) | — |
| B | 0.2380 | 6.045 | 15/64" (0.2344) · 6.0 mm (0.2362) | — |
| C | 0.2420 | 6.147 | 15/64" (0.2344) · 6.1 mm (0.2402) | — |
| D | 0.2460 | 6.248 | 1/4" (0.2500) · 6.2 mm (0.2441) | — |
| E | 0.2500 | 6.350 | 1/4" (0.2500) · 6.3 mm (0.2480) | — |
| F | 0.2570 | 6.528 | 1/4" (0.2500) · 6.5 mm (0.2559) | 5/16-18 |
| G | 0.2610 | 6.629 | 17/64" (0.2656) · 6.6 mm (0.2598) | — |
| H | 0.2660 | 6.756 | 17/64" (0.2656) · 6.8 mm (0.2677) | — |
| I | 0.2720 | 6.909 | 17/64" (0.2656) · 6.9 mm (0.2717) | 5/16-24 |
| J | 0.2770 | 7.036 | 9/32" (0.2813) · 7.0 mm (0.2756) | 5/16-18 (50%) |
| K | 0.2810 | 7.137 | 9/32" (0.2813) · 7.1 mm (0.2795) | — |
| L | 0.2900 | 7.366 | 19/64" (0.2969) · 7.4 mm (0.2913) | 5/16-18 (form), 5/16-32 (50%) |
| M | 0.2950 | 7.493 | 19/64" (0.2969) · 7.5 mm (0.2953) | 5/16-24 (form) |
| N | 0.3020 | 7.671 | 19/64" (0.2969) · 7.7 mm (0.3031) | — |
| O | 0.3160 | 8.026 | 5/16" (0.3125) · 8.0 mm (0.3150) | — |
| P | 0.3230 | 8.204 | 21/64" (0.3281) · 8.2 mm (0.3228) | — |
| Q | 0.3320 | 8.433 | 21/64" (0.3281) · 8.4 mm (0.3307) | 3/8-24, 3/8-16 (50%) |
| R | 0.3390 | 8.611 | 11/32" (0.3438) · 8.6 mm (0.3386) | — |
| S | 0.3480 | 8.839 | 11/32" (0.3438) · 8.8 mm (0.3465) | 3/8-16 (form), 3/8-24 (50%) |
| T | 0.3580 | 9.093 | 23/64" (0.3594) · 9.1 mm (0.3583) | 3/8-24 (form), 3/8-32 (50%) |
| U | 0.3680 | 9.347 | 3/8" (0.3750) · 9.3 mm (0.3661) | 7/16-14 |
| V | 0.3770 | 9.576 | 3/8" (0.3750) · 9.6 mm (0.3780) | — |
| W | 0.3860 | 9.804 | 25/64" (0.3906) · 9.8 mm (0.3858) | — |
| X | 0.3970 | 10.084 | 25/64" (0.3906) · 10.1 mm (0.3976) | — |
| Y | 0.4040 | 10.262 | 13/32" (0.4063) · 10.3 mm (0.4055) | 7/16-28, 7/16-20 (50%) |
| Z | 0.4130 | 10.490 | 13/32" (0.4063) · 10.5 mm (0.4134) | 7/16-20 (form), 7/16-28 (50%) |
Common questions
- What size is a letter F drill?
- 0.257 in (6.528 mm), the 5/16-18 tap drill.
- What is the largest letter drill?
- Z, at 0.413 in (10.490 mm).
- Is a letter E drill 1/4 inch?
- Yes. E is 0.250 in, the same as a 1/4 in fractional drill.
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