Tap Drill Chart
The correct drill for every common inch and metric tap. Inch sizes give about 75% thread engagement, the standard for most tapped holes; metric sizes use the diameter-minus-pitch rule. Drill diameters are shown in both inches and millimeters.
Inch tap drill chart (UNC & UNF)
| Tap size | Series | Major dia. (in) | Tap drill | Drill (in) | Drill (mm) |
|---|---|---|---|---|---|
| #0-80 | UNF | 0.0600 | 3/64" | 0.0469 | 1.191 |
| #1-64 | UNC | 0.0730 | #53 | 0.0595 | 1.511 |
| #1-72 | UNF | 0.0730 | #53 | 0.0595 | 1.511 |
| #2-56 | UNC | 0.0860 | #50 | 0.0700 | 1.778 |
| #2-64 | UNF | 0.0860 | #50 | 0.0700 | 1.778 |
| #3-48 | UNC | 0.0990 | #47 | 0.0785 | 1.994 |
| #3-56 | UNF | 0.0990 | #45 | 0.0820 | 2.083 |
| #4-40 | UNC | 0.1120 | #43 | 0.0890 | 2.261 |
| #4-48 | UNF | 0.1120 | #42 | 0.0935 | 2.375 |
| #5-40 | UNC | 0.1250 | #38 | 0.1015 | 2.578 |
| #5-44 | UNF | 0.1250 | #37 | 0.1040 | 2.642 |
| #6-32 | UNC | 0.1380 | #36 | 0.1065 | 2.705 |
| #6-40 | UNF | 0.1380 | #33 | 0.1130 | 2.870 |
| #8-32 | UNC | 0.1640 | #29 | 0.1360 | 3.454 |
| #8-36 | UNF | 0.1640 | #29 | 0.1360 | 3.454 |
| #10-24 | UNC | 0.1900 | #25 | 0.1495 | 3.797 |
| #10-32 | UNF | 0.1900 | #21 | 0.1590 | 4.039 |
| #12-24 | UNC | 0.2160 | #16 | 0.1770 | 4.496 |
| 1/4-20 | UNC | 0.2500 | #7 | 0.2010 | 5.105 |
| 1/4-28 | UNF | 0.2500 | #3 | 0.2130 | 5.410 |
| 5/16-18 | UNC | 0.3125 | F | 0.2570 | 6.528 |
| 5/16-24 | UNF | 0.3125 | I | 0.2720 | 6.909 |
| 3/8-16 | UNC | 0.3750 | 5/16" | 0.3125 | 7.938 |
| 3/8-24 | UNF | 0.3750 | Q | 0.3320 | 8.433 |
| 7/16-14 | UNC | 0.4375 | U | 0.3680 | 9.347 |
| 7/16-20 | UNF | 0.4375 | 25/64" | 0.3906 | 9.922 |
| 1/2-13 | UNC | 0.5000 | 27/64" | 0.4219 | 10.716 |
| 1/2-20 | UNF | 0.5000 | 29/64" | 0.4531 | 11.509 |
| 9/16-12 | UNC | 0.5625 | 31/64" | 0.4844 | 12.303 |
| 9/16-18 | UNF | 0.5625 | 33/64" | 0.5156 | 13.097 |
| 5/8-11 | UNC | 0.6250 | 17/32" | 0.5313 | 13.494 |
| 5/8-18 | UNF | 0.6250 | 37/64" | 0.5781 | 14.684 |
| 3/4-10 | UNC | 0.7500 | 21/32" | 0.6563 | 16.669 |
| 3/4-16 | UNF | 0.7500 | 11/16" | 0.6875 | 17.462 |
| 7/8-9 | UNC | 0.8750 | 49/64" | 0.7656 | 19.447 |
| 7/8-14 | UNF | 0.8750 | 13/16" | 0.8125 | 20.637 |
| 1-8 | UNC | 1.0000 | 7/8" | 0.8750 | 22.225 |
| 1-12 | UNF | 1.0000 | 59/64" | 0.9219 | 23.416 |
UNC = Unified National Coarse, UNF = Unified National Fine. “1/4-20” means a 1/4 in diameter with 20 threads per inch.
Metric tap drill chart (coarse threads)
| Tap size | Pitch (mm) | Tap drill (mm) | Tap drill (in) |
|---|---|---|---|
| M1.6 × 0.35 | 0.35 | 1.25 mm | 0.0492 |
| M2 × 0.4 | 0.4 | 1.6 mm | 0.0630 |
| M2.5 × 0.45 | 0.45 | 2.05 mm | 0.0807 |
| M3 × 0.5 | 0.5 | 2.5 mm | 0.0984 |
| M3.5 × 0.6 | 0.6 | 2.9 mm | 0.1142 |
| M4 × 0.7 | 0.7 | 3.3 mm | 0.1299 |
| M5 × 0.8 | 0.8 | 4.2 mm | 0.1654 |
| M6 × 1 | 1 | 5 mm | 0.1969 |
| M7 × 1 | 1 | 6 mm | 0.2362 |
| M8 × 1.25 | 1.25 | 6.75 mm | 0.2657 |
| M10 × 1.5 | 1.5 | 8.5 mm | 0.3346 |
| M12 × 1.75 | 1.75 | 10.25 mm | 0.4035 |
| M14 × 2 | 2 | 12 mm | 0.4724 |
| M16 × 2 | 2 | 14 mm | 0.5512 |
| M18 × 2.5 | 2.5 | 15.5 mm | 0.6102 |
| M20 × 2.5 | 2.5 | 17.5 mm | 0.6890 |
| M22 × 2.5 | 2.5 | 19.5 mm | 0.7677 |
| M24 × 3 | 3 | 21 mm | 0.8268 |
Where the result falls between bit sizes (M2.5 → 2.05 mm, M8 → 6.75 mm), use the nearest standard bit: 2.05 or 2.1 mm, and 6.8 mm.
How to tap a hole
- Center-punch the spot so the drill does not wander.
- Drill with the tap drill from the chart. Find its exact size in the drill bit size chart.
- Chamfer the hole slightly so the tap starts straight.
- Use cutting fluid, turn the tap in, and back it off about a half turn every one or two turns to break the chip.
Tap Drill Chart FAQ
What size drill do I use for a 1/4-20 tap?
Use a #7 drill (0.201 in, 5.105 mm). It gives about 75% thread depth, which is the standard for general-purpose tapped holes. A 13/64 in bit (0.2031 in) is a common substitute.
What is the tap drill size for M6 and M8?
For an M6 × 1.0 coarse thread, use a 5 mm drill. For M8 × 1.25, use a 6.8 mm drill (the exact major-minus-pitch value is 6.75 mm, and 6.8 mm is the standard bit).
How do I calculate a tap drill size?
Subtract the thread pitch from the major diameter. For metric threads that is simply diameter minus pitch, e.g. M10 × 1.5 → 8.5 mm. For inch threads, the pitch is 1 ÷ threads per inch: 1/2-13 → 0.500 − 0.077 = 0.423 in, so a 27/64 in (0.4219 in) drill.
Why 75% thread and not 100%?
A 75% thread is only slightly weaker than a full thread but takes much less torque to tap, so taps break far less often. In hard materials or deep holes, a slightly larger drill (around 60–65% thread) is common.
Sources
Inch pairings appear in both the Micro Precision “Tap Drill Sizes for a 75% Thread” table and Wikipedia's “List of drill and tap sizes” (#10-32, #12-24, and 1/4-20 from the latter). Numbered screw diameters are 0.060 + 0.013 × N in (ASME B1.1). Metric coarse pitches are from ISO 261.