Tap Drill Size Chart
Tap drill sizes for 214 threads: ISO metric coarse and fine, UNC, UNF, UNEF, NPT and BSP. Each drill is given in millimetres and inches with the percentage of thread it leaves.
ISO metric coarse tap drills
| Thread | Tap drill (mm) | Drill (in) | % thread | Minor Ø D1 (mm) |
|---|---|---|---|---|
| M1×0.25 | 0.75 | 0.0295 | 77% | 0.729 |
| M1.2×0.25 | 0.95 | 0.0374 | 77% | 0.929 |
| M1.4×0.3 | 1.1 | 0.0433 | 77% | 1.075 |
| M1.6×0.35 | 1.25 | 0.0492 | 77% | 1.221 |
| M1.8×0.35 | 1.45 | 0.0571 | 77% | 1.421 |
| M2×0.4 | 1.6 | 0.0630 | 77% | 1.567 |
| M2.5×0.45 | 2.05 | 0.0807 | 77% | 2.013 |
| M3×0.5 | 2.5 | 0.0984 | 77% | 2.459 |
| M3.5×0.6 | 2.9 | 0.1142 | 77% | 2.850 |
| M4×0.7 | 3.3 | 0.1299 | 77% | 3.242 |
| M5×0.8 | 4.2 | 0.1654 | 77% | 4.134 |
| M6×1 | 5 | 0.1969 | 77% | 4.917 |
| M7×1 | 6 | 0.2362 | 77% | 5.917 |
| M8×1.25 | 6.8 | 0.2677 | 74% | 6.647 |
| M9×1.25 | 7.8 | 0.3071 | 74% | 7.647 |
| M10×1.5 | 8.5 | 0.3346 | 77% | 8.376 |
| M12×1.75 | 10.2 | 0.4016 | 79% | 10.106 |
| M14×2 | 12 | 0.4724 | 77% | 11.835 |
| M16×2 | 14 | 0.5512 | 77% | 13.835 |
| M18×2.5 | 15.5 | 0.6102 | 77% | 15.294 |
| M20×2.5 | 17.5 | 0.6890 | 77% | 17.294 |
| M22×2.5 | 19.5 | 0.7677 | 77% | 19.294 |
| M24×3 | 21 | 0.8268 | 77% | 20.752 |
| M27×3 | 24 | 0.9449 | 77% | 23.752 |
| M30×3.5 | 26.5 | 1.0433 | 77% | 26.211 |
| M33×3.5 | 29.5 | 1.1614 | 77% | 29.211 |
| M36×4 | 32 | 1.2598 | 77% | 31.670 |
| M39×4 | 35 | 1.3780 | 77% | 34.670 |
| M42×4.5 | 37.5 | 1.4764 | 77% | 37.129 |
| M45×4.5 | 40.5 | 1.5945 | 77% | 40.129 |
| M48×5 | 43 | 1.6929 | 77% | 42.587 |
| M52×5 | 47 | 1.8504 | 77% | 46.587 |
| M56×5.5 | 50.5 | 1.9882 | 77% | 50.046 |
| M60×5.5 | 54.5 | 2.1457 | 77% | 54.046 |
| M64×6 | 58 | 2.2835 | 77% | 57.505 |
| M68×6 | 62 | 2.4409 | 77% | 61.505 |
ISO metric fine tap drills
| Thread | Tap drill (mm) | Drill (in) | % thread | Minor Ø D1 (mm) |
|---|---|---|---|---|
| M3×0.35 | 2.65 | 0.1043 | 77% | 2.621 |
| M4×0.5 | 3.5 | 0.1378 | 77% | 3.459 |
| M5×0.5 | 4.5 | 0.1772 | 77% | 4.459 |
| M6×0.75 | 5.2 | 0.2047 | 82% | 5.188 |
| M7×0.75 | 6.2 | 0.2441 | 82% | 6.188 |
| M8×0.75 | 7.2 | 0.2835 | 82% | 7.188 |
| M8×1 | 7 | 0.2756 | 77% | 6.917 |
| M9×1 | 8 | 0.3150 | 77% | 7.917 |
| M10×0.75 | 9.2 | 0.3622 | 82% | 9.188 |
| M10×1 | 9 | 0.3543 | 77% | 8.917 |
| M10×1.25 | 8.8 | 0.3465 | 74% | 8.647 |
| M12×1 | 11 | 0.4331 | 77% | 10.917 |
| M12×1.25 | 10.8 | 0.4252 | 74% | 10.647 |
| M12×1.5 | 10.5 | 0.4134 | 77% | 10.376 |
| M14×1 | 13 | 0.5118 | 77% | 12.917 |
| M14×1.25 | 12.8 | 0.5039 | 74% | 12.647 |
| M14×1.5 | 12.5 | 0.4921 | 77% | 12.376 |
| M16×1 | 15 | 0.5906 | 77% | 14.917 |
| M16×1.25 | 14.8 | 0.5827 | 74% | 14.647 |
| M16×1.5 | 14.5 | 0.5709 | 77% | 14.376 |
| M18×1 | 17 | 0.6693 | 77% | 16.917 |
| M18×1.5 | 16.5 | 0.6496 | 77% | 16.376 |
| M18×2 | 16 | 0.6299 | 77% | 15.835 |
| M20×1 | 19 | 0.7480 | 77% | 18.917 |
| M20×1.5 | 18.5 | 0.7283 | 77% | 18.376 |
| M20×2 | 18 | 0.7087 | 77% | 17.835 |
| M22×1 | 21 | 0.8268 | 77% | 20.917 |
| M22×1.5 | 20.5 | 0.8071 | 77% | 20.376 |
| M22×2 | 20 | 0.7874 | 77% | 19.835 |
| M24×1 | 23 | 0.9055 | 77% | 22.917 |
| M24×1.5 | 22.5 | 0.8858 | 77% | 22.376 |
| M24×2 | 22 | 0.8661 | 77% | 21.835 |
| M27×1 | 26 | 1.0236 | 77% | 25.917 |
| M27×1.5 | 25.5 | 1.0039 | 77% | 25.376 |
| M27×2 | 25 | 0.9843 | 77% | 24.835 |
| M30×1 | 29 | 1.1417 | 77% | 28.917 |
| M30×1.5 | 28.5 | 1.1220 | 77% | 28.376 |
| M30×2 | 28 | 1.1024 | 77% | 27.835 |
| M33×1.5 | 31.5 | 1.2402 | 77% | 31.376 |
| M33×2 | 31 | 1.2205 | 77% | 30.835 |
| M33×3 | 30 | 1.1811 | 77% | 29.752 |
| M36×1.5 | 34.5 | 1.3583 | 77% | 34.376 |
| M36×2 | 34 | 1.3386 | 77% | 33.835 |
| M36×3 | 33 | 1.2992 | 77% | 32.752 |
| M39×1.5 | 37.5 | 1.4764 | 77% | 37.376 |
| M39×2 | 37 | 1.4567 | 77% | 36.835 |
| M39×3 | 36 | 1.4173 | 77% | 35.752 |
| M42×1.5 | 40.5 | 1.5945 | 77% | 40.376 |
| M42×2 | 40 | 1.5748 | 77% | 39.835 |
| M42×3 | 39 | 1.5354 | 77% | 38.752 |
| M45×1.5 | 43.5 | 1.7126 | 77% | 43.376 |
| M45×2 | 43 | 1.6929 | 77% | 42.835 |
| M45×3 | 42 | 1.6535 | 77% | 41.752 |
| M48×1.5 | 46.5 | 1.8307 | 77% | 46.376 |
| M48×2 | 46 | 1.8110 | 77% | 45.835 |
| M48×3 | 45 | 1.7717 | 77% | 44.752 |
For 0.75 mm and 1.25 mm pitches, tables round diameter minus pitch to a 0.1 mm drill (8.75 becomes 8.8); either size works. Full metric fine chart
UNC tap drills
| Thread | Tap drill | Drill (in) | Drill (mm) | % thread | Minor Ø D1 (in) |
|---|---|---|---|---|---|
| #1-64 UNC | #53 | 0.0595 | 1.51 | 67% | 0.0561 |
| #2-56 UNC | #50 | 0.0700 | 1.78 | 69% | 0.0667 |
| #3-48 UNC | #47 | 0.0785 | 1.99 | 76% | 0.0764 |
| #4-40 UNC | #43 | 0.0890 | 2.26 | 71% | 0.0849 |
| #5-40 UNC | #38 | 0.1015 | 2.58 | 72% | 0.0979 |
| #6-32 UNC | #36 | 0.1065 | 2.71 | 78% | 0.1042 |
| #8-32 UNC | #29 | 0.1360 | 3.45 | 69% | 0.1302 |
| #10-24 UNC | #25 | 0.1495 | 3.80 | 75% | 0.1449 |
| #12-24 UNC | #16 | 0.1770 | 4.50 | 72% | 0.1709 |
| 1/4-20 UNC | #7 | 0.2010 | 5.11 | 75% | 0.1959 |
| 5/16-18 UNC | F | 0.2570 | 6.53 | 77% | 0.2524 |
| 3/8-16 UNC | 5/16" | 0.3125 | 7.94 | 77% | 0.3073 |
| 7/16-14 UNC | U | 0.3680 | 9.35 | 75% | 0.3602 |
| 1/2-13 UNC | 27/64" | 0.4219 | 10.72 | 78% | 0.4167 |
| 9/16-12 UNC | 31/64" | 0.4844 | 12.30 | 72% | 0.4723 |
| 5/8-11 UNC | 17/32" | 0.5312 | 13.49 | 79% | 0.5266 |
| 3/4-10 UNC | 21/32" | 0.6562 | 16.67 | 72% | 0.6417 |
| 7/8-9 UNC | 49/64" | 0.7656 | 19.45 | 76% | 0.7547 |
| 1-8 UNC | 7/8" | 0.8750 | 22.22 | 77% | 0.8647 |
| 1-1/8-7 UNC | 63/64" | 0.9844 | 25.00 | 76% | 0.9704 |
| 1-1/4-7 UNC | 1-7/64" | 1.1094 | 28.18 | 76% | 1.0954 |
| 1-3/8-6 UNC | 1-7/32" | 1.2188 | 30.96 | 72% | 1.1946 |
| 1-1/2-6 UNC | 1-11/32" | 1.3438 | 34.13 | 72% | 1.3196 |
| 1-3/4-5 UNC | 1-9/16" | 1.5625 | 39.69 | 72% | 1.5335 |
| 2-4.5 UNC | 1-25/32" | 1.7812 | 45.24 | 76% | 1.7594 |
| 2-1/4-4.5 UNC | 2-1/32" | 2.0312 | 51.59 | 76% | 2.0094 |
| 2-1/2-4 UNC | 2-1/4" | 2.2500 | 57.15 | 77% | 2.2294 |
| 2-3/4-4 UNC | 2-1/2" | 2.5000 | 63.50 | 77% | 2.4794 |
| 3-4 UNC | 2-3/4" | 2.7500 | 69.85 | 77% | 2.7294 |
| 3-1/4-4 UNC | 3" | 3.0000 | 76.20 | 77% | 2.9794 |
| 3-1/2-4 UNC | 3-1/4" | 3.2500 | 82.55 | 77% | 3.2294 |
| 3-3/4-4 UNC | 3-1/2" | 3.5000 | 88.90 | 77% | 3.4794 |
| 4-4 UNC | 3-3/4" | 3.7500 | 95.25 | 77% | 3.7294 |
UNF tap drills
| Thread | Tap drill | Drill (in) | Drill (mm) | % thread | Minor Ø D1 (in) |
|---|---|---|---|---|---|
| #0-80 UNF | 3/64" | 0.0469 | 1.19 | 81% | 0.0465 |
| #1-72 UNF | #53 | 0.0595 | 1.51 | 75% | 0.0580 |
| #2-64 UNF | #50 | 0.0700 | 1.78 | 79% | 0.0691 |
| #3-56 UNF | #45 | 0.0820 | 2.08 | 73% | 0.0797 |
| #4-48 UNF | #42 | 0.0935 | 2.37 | 68% | 0.0894 |
| #5-44 UNF | #37 | 0.1040 | 2.64 | 71% | 0.1004 |
| #6-40 UNF | #33 | 0.1130 | 2.87 | 77% | 0.1109 |
| #8-36 UNF | #29 | 0.1360 | 3.45 | 78% | 0.1339 |
| #10-32 UNF | #21 | 0.1590 | 4.04 | 76% | 0.1562 |
| #12-28 UNF | #14 | 0.1820 | 4.62 | 73% | 0.1773 |
| 1/4-28 UNF | #3 | 0.2130 | 5.41 | 80% | 0.2113 |
| 5/16-24 UNF | I | 0.2720 | 6.91 | 75% | 0.2674 |
| 3/8-24 UNF | Q | 0.3320 | 8.43 | 79% | 0.3299 |
| 7/16-20 UNF | 25/64" | 0.3906 | 9.92 | 72% | 0.3834 |
| 1/2-20 UNF | 29/64" | 0.4531 | 11.51 | 72% | 0.4459 |
| 9/16-18 UNF | 33/64" | 0.5156 | 13.10 | 65% | 0.5024 |
| 5/8-18 UNF | 37/64" | 0.5781 | 14.68 | 65% | 0.5649 |
| 3/4-16 UNF | 11/16" | 0.6875 | 17.46 | 77% | 0.6823 |
| 7/8-14 UNF | 13/16" | 0.8125 | 20.64 | 67% | 0.7977 |
| 1-12 UNF | 59/64" | 0.9219 | 23.42 | 72% | 0.9098 |
| 1-1/8-12 UNF | 1-3/64" | 1.0469 | 26.59 | 72% | 1.0348 |
| 1-1/4-12 UNF | 1-11/64" | 1.1719 | 29.77 | 72% | 1.1598 |
| 1-3/8-12 UNF | 1-19/64" | 1.2969 | 32.94 | 72% | 1.2848 |
| 1-1/2-12 UNF | 1-27/64" | 1.4219 | 36.12 | 72% | 1.4098 |
UNEF tap drills
| Thread | Tap drill | Drill (in) | Drill (mm) | % thread | Minor Ø D1 (in) |
|---|---|---|---|---|---|
| #12-32 UNEF | #13 | 0.1850 | 4.70 | 76% | 0.1822 |
| 1/4-32 UNEF | 7/32" | 0.2188 | 5.56 | 77% | 0.2162 |
| 5/16-32 UNEF | 9/32" | 0.2812 | 7.14 | 77% | 0.2787 |
| 3/8-32 UNEF | 11/32" | 0.3438 | 8.73 | 77% | 0.3412 |
| 7/16-28 UNEF | Y | 0.4040 | 10.26 | 72% | 0.3988 |
| 1/2-28 UNEF | 15/32" | 0.4688 | 11.91 | 67% | 0.4613 |
| 9/16-24 UNEF | 33/64" | 0.5156 | 13.10 | 87% | 0.5174 |
| 5/8-24 UNEF | 37/64" | 0.5781 | 14.68 | 87% | 0.5799 |
| 11/16-24 UNEF | 41/64" | 0.6406 | 16.27 | 87% | 0.6424 |
| 3/4-20 UNEF | 45/64" | 0.7031 | 17.86 | 72% | 0.6959 |
| 13/16-20 UNEF | 49/64" | 0.7656 | 19.45 | 72% | 0.7584 |
| 7/8-20 UNEF | 53/64" | 0.8281 | 21.03 | 72% | 0.8209 |
| 15/16-20 UNEF | 57/64" | 0.8906 | 22.62 | 72% | 0.8834 |
| 1-20 UNEF | 61/64" | 0.9531 | 24.21 | 72% | 0.9459 |
| 1-1/16-18 UNEF | 1-1/64" | 1.0156 | 25.80 | 65% | 1.0024 |
| 1-1/8-18 UNEF | 1-5/64" | 1.0781 | 27.38 | 65% | 1.0649 |
| 1-3/16-18 UNEF | 1-9/64" | 1.1406 | 28.97 | 65% | 1.1274 |
| 1-1/4-18 UNEF | 1-13/64" | 1.2031 | 30.56 | 65% | 1.1899 |
| 1-5/16-18 UNEF | 1-17/64" | 1.2656 | 32.15 | 65% | 1.2524 |
| 1-3/8-18 UNEF | 1-21/64" | 1.3281 | 33.73 | 65% | 1.3149 |
| 1-7/16-18 UNEF | 1-25/64" | 1.3906 | 35.32 | 65% | 1.3774 |
| 1-1/2-18 UNEF | 1-29/64" | 1.4531 | 36.91 | 65% | 1.4399 |
| 1-9/16-18 UNEF | 1-33/64" | 1.5156 | 38.50 | 65% | 1.5024 |
| 1-5/8-18 UNEF | 1-37/64" | 1.5781 | 40.08 | 65% | 1.5649 |
| 1-11/16-18 UNEF | 1-41/64" | 1.6406 | 41.67 | 65% | 1.6274 |
NPT tap drills
| Thread | Tap drill | Drill (in) | Drill (mm) | ASME B1.20.1, no reaming | ASME B1.20.1, before reaming | Minor Ø K0 (in) |
|---|---|---|---|---|---|---|
| 1/16-27 NPT | D | 0.2460 | 6.25 | C | A | 0.2416 |
| 1/8-27 NPT | R | 0.3390 | 8.61 | Q | 21/64" | 0.3339 |
| 1/4-18 NPT | 7/16" | 0.4375 | 11.11 | 7/16" | 27/64" | 0.4329 |
| 3/8-18 NPT | 37/64" | 0.5781 | 14.68 | 9/16" | 9/16" | 0.5676 |
| 1/2-14 NPT | 23/32" | 0.7188 | 18.26 | 45/64" | 11/16" | 0.7013 |
| 3/4-14 NPT | 59/64" | 0.9219 | 23.42 | 29/32" | 57/64" | 0.9105 |
| 1-11.5 NPT | 1-5/32" | 1.1562 | 29.37 | 1-9/64" | 1-1/8" | 1.1441 |
| 1-1/4-11.5 NPT | 1-1/2" | 1.5000 | 38.10 | 1-31/64" | 1-15/32" | 1.4876 |
| 1-1/2-11.5 NPT | 1-47/64" | 1.7344 | 44.05 | 1-23/32" | 1-45/64" | 1.7265 |
| 2-11.5 NPT | 2-7/32" | 2.2188 | 56.36 | 2-3/16" | 2-11/64" | 2.1995 |
| 2-1/2-8 NPT | 2-5/8" | 2.6250 | 66.67 | 2-39/64" | 2-37/64" | 2.6195 |
| 3-8 NPT | 3-1/4" | 3.2500 | 82.55 | — | — | 3.2406 |
| 3-1/2-8 NPT | 3-3/4" | 3.7500 | 95.25 | — | — | 3.7375 |
| 4-8 NPT | 4-1/4" | 4.2500 | 107.95 | — | — | 4.2344 |
| 5-8 NPT | 5-5/16" | 5.3125 | 134.94 | — | — | 5.2907 |
| 6-8 NPT | 6-3/8" | 6.3750 | 161.92 | — | — | 6.3461 |
| 8-8 NPT | — | — | — | — | — | 8.3336 |
| 10-8 NPT | — | — | — | — | — | 10.4453 |
| 12-8 NPT | — | — | — | — | — | 12.4328 |
BSP (G) tap drills
| Thread | Tap drill (mm) | Drill (in) | % thread | Minor Ø (mm) |
|---|---|---|---|---|
| G1/16 | 6.8 | 0.2677 | 79% | 6.561 |
| G1/8 | 8.8 | 0.3465 | 80% | 8.566 |
| G1/4 | 11.8 | 0.4646 | 79% | 11.445 |
| G3/8 | 15.25 | 0.6004 | 82% | 14.950 |
| G1/2 | 19 | 0.7480 | 84% | 18.632 |
| G5/8 | 21 | 0.8268 | 82% | 20.588 |
| G3/4 | 24.5 | 0.9646 | 84% | 24.118 |
| G7/8 | 28.25 | 1.1122 | 84% | 27.878 |
| G1 | 30.75 | 1.2106 | 85% | 30.292 |
| G1-1/8 | 35.5 | 1.3976 | 81% | 34.940 |
| G1-1/4 | 39.5 | 1.5551 | 81% | 38.953 |
| G1-3/8 | 41.75 | 1.6437 | 87% | 41.366 |
| G1-1/2 | 45.25 | 1.7815 | 86% | 44.846 |
| G1-3/4 | 51 | 2.0079 | 93% | 50.789 |
| G2 | 57 | 2.2441 | 88% | 56.657 |
| G2-1/4 | 63.3 | 2.4921 | 81% | 62.753 |
| G2-1/2 | 72.8 | 2.8661 | 81% | 72.227 |
| G2-3/4 | 79.1 | 3.1142 | 82% | 78.577 |
| G3 | 85.5 | 3.3661 | 81% | 84.927 |
| G3-1/2 | 97.7 | 3.8465 | 89% | 97.373 |
| G4 | 110.4 | 4.3465 | 89% | 110.073 |
What percentage of thread to use
The percentage of thread says how much of the full thread height is left in the hole. It is set only by the drill: a larger drill leaves less. The convention measures it against a height of 0.6495 × pitch, so
% thread = (major diameter − drill diameter) ÷ (1.299 × pitch) × 100
and, turned around, drill = major diameter − % × 1.299 × pitch.
Standard tap drills sit at 70 to 80%. The metric rule of diameter minus pitch gives exactly 77%, or a little less once it is rounded up to a stocked drill. Going above 80% raises the tapping torque sharply and gains very little strength, because in a nut of normal height the bolt usually breaks before a 60% thread strips. Going below 60% starts to cost strength.
| % thread | Drill for M8×1.25 (mm) | Thread height left (mm) | Typical use |
|---|---|---|---|
| 100% | 6.38 | 0.812 | hole below the minimum minor Ø: not usable |
| 90% | 6.54 | 0.731 | hole below the minimum minor Ø: not usable |
| 83% | 6.65 | 0.674 | basic minor Ø, the smallest allowed hole |
| 77% | 6.75 | 0.625 | standard tap drill (diameter minus pitch) |
| 70% | 6.86 | 0.568 | easier tapping, general work |
| 65% | 6.94 | 0.528 | stainless, tough alloys, deep holes |
| 60% | 7.03 | 0.487 | stainless, tough alloys, deep holes |
| 50% | 7.19 | 0.406 | thin sheet only |
Three practical rules: use the charted drill in mild steel, brass and aluminium; go one drill size larger in stainless steel, titanium and hardened material; and check that the hole stays inside the minor diameter limits of the thread class, which each thread page lists.
Thread-forming (roll) taps displace metal instead of cutting it and need a larger hole, close to the pitch diameter. The drills in this chart are for cutting taps only.
Common questions
What size drill for an M6 tap?
A 5 mm drill. M6×1 coarse: 6 − 1 = 5 mm, which leaves 77% thread.
What size drill for a 1/4-20 tap?
A #7 drill, 0.2010 in (5.11 mm). A 13/64 in drill (0.2031 in) is the nearest fractional size and leaves about 72% thread.
Can I use a slightly larger drill than the chart says?
Yes, within limits. One drill size larger typically drops the thread from about 77% to 65 to 70%, which costs little strength and makes tapping much easier. Stay inside the minor diameter limits given on the thread page.
Other charts and tools
Sources: tap drill tables based on ISO 2306, Machinery’s Handbook, ASME B1.20.1 Appendix and tap manufacturers’ charts. How this site checks its data. Last reviewed 29 September 2026.