TorqueMath.com · Tap Drill Charttorquemath.com/tap-drill-chart/
Use this chart when you need the drill for a tapped hole. The cutting-tap column gives the drill for about 77 % thread, the usual choice in steel; the thread % column shows what that drill actually gives, and the minor-diameter column shows the band the hole has to stay in for the thread gauge to pass. Forming (roll) taps push the metal into the thread instead of cutting it, so they need a larger hole – use their own column. For metric screws the chart also lists the clearance hole for the part the screw passes through.
Metric coarse thread (ISO 261)
| Thread | Pitch mm | Cutting tap · 77 % | Forming tap · 65 % | Clearance hole ISO 273, mm | |||||
|---|---|---|---|---|---|---|---|---|---|
| Drill mm | Thread % | 6H minor Ø mm | Drill mm | Thread % | close | normal | loose | ||
| M1.6 | 0.35 | 1.25 | 77 % | 1.221 – 1.321 | 1.45 | 63 % | 1.7 | 1.8 | 2 |
| M2 | 0.4 | 1.60 | 77 % | 1.567 – 1.679 | 1.80 | 74 % | 2.2 | 2.4 | 2.6 |
| M2.5 | 0.45 | 2.05 | 77 % | 2.013 – 2.138 | 2.30 | 65 % | 2.7 | 2.9 | 3.1 |
| M3 | 0.5 | 2.50 | 77 % | 2.459 – 2.599 | 2.80 | 59 % | 3.2 | 3.4 | 3.6 |
| M3.5 | 0.6 | 2.90 | 77 % | 2.851 – 3.011 | 3.2 | 74 % | 3.7 | 3.9 | 4.2 |
| M4 | 0.7 | 3.3 | 77 % | 3.242 – 3.422 | 3.7 | 63 % | 4.3 | 4.5 | 4.8 |
| M5 | 0.8 | 4.2 | 77 % | 4.134 – 4.334 | 4.6 | 74 % | 5.3 | 5.5 | 5.8 |
| M6 | 1 | 5.0 | 77 % | 4.918 – 5.154 | 5.6 | 59 % | 6.4 | 6.6 | 7 |
| M8 | 1.25 | 6.8 | 74 % | 6.647 – 6.912 | 7.4 | 71 % | 8.4 | 9 | 10 |
| M10 | 1.5 | 8.5 | 77 % | 8.376 – 8.676 | 9.3 | 69 % | 10.5 | 11 | 12 |
| M12 | 1.75 | 10.2 | 79 % | 10.106 – 10.441 | 11.2 | 67 % | 13 | 13.5 | 14.5 |
| M14 | 2 | 12.0 | 77 % | 11.835 – 12.210 | 13.1 | 66 % | 15 | 15.5 | 16.5 |
| M16 | 2 | 14.0 | 77 % | 13.835 – 14.210 | 15.1 | 66 % | 17 | 17.5 | 18.5 |
| M18 | 2.5 | 15.5 | 77 % | 15.294 – 15.744 | 16.9 | 65 % | 19 | 20 | 21 |
| M20 | 2.5 | 17.5 | 77 % | 17.294 – 17.744 | 18.9 | 65 % | 21 | 22 | 24 |
| M22 | 2.5 | 19.5 | 77 % | 19.294 – 19.744 | 20.9 | 65 % | 23 | 24 | 26 |
| M24 | 3 | 21.0 | 77 % | 20.753 – 21.253 | 22.7 | 64 % | 25 | 26 | 28 |
| M27 | 3 | 24.0 | 77 % | 23.753 – 24.253 | 25.7 | 64 % | 28 | 30 | 32 |
| M30 | 3.5 | 26.5 | 77 % | 26.211 – 26.771 | 28.5 | 63 % | 31 | 33 | 35 |
| M36 | 4 | 32.0 | 77 % | 31.670 – 32.270 | 34.2 | 66 % | 37 | 39 | 42 |
Metric fine thread
| Thread | Pitch mm | Cutting tap · 77 % | Forming tap · 65 % | Clearance hole ISO 273, mm | |||||
|---|---|---|---|---|---|---|---|---|---|
| Drill mm | Thread % | 6H minor Ø mm | Drill mm | Thread % | close | normal | loose | ||
| M8×1 | 1 | 7.0 | 77 % | 6.918 – 7.154 | 7.6 | 59 % | 8.4 | 9 | 10 |
| M10×1 | 1 | 9.0 | 77 % | 8.918 – 9.154 | 9.6 | 59 % | 10.5 | 11 | 12 |
| M10×1.25 | 1.25 | 8.8 | 74 % | 8.647 – 8.912 | 9.4 | 71 % | 10.5 | 11 | 12 |
| M12×1.25 | 1.25 | 10.8 | 74 % | 10.647 – 10.912 | 11.4 | 71 % | 13 | 13.5 | 14.5 |
| M12×1.5 | 1.5 | 10.5 | 77 % | 10.376 – 10.676 | 11.3 | 69 % | 13 | 13.5 | 14.5 |
| M14×1.5 | 1.5 | 12.5 | 77 % | 12.376 – 12.676 | 13.3 | 69 % | 15 | 15.5 | 16.5 |
| M16×1.5 | 1.5 | 14.5 | 77 % | 14.376 – 14.676 | 15.3 | 69 % | 17 | 17.5 | 18.5 |
| M18×1.5 | 1.5 | 16.5 | 77 % | 16.376 – 16.676 | 17.3 | 69 % | 19 | 20 | 21 |
| M20×1.5 | 1.5 | 18.5 | 77 % | 18.376 – 18.676 | 19.3 | 69 % | 21 | 22 | 24 |
| M22×1.5 | 1.5 | 20.5 | 77 % | 20.376 – 20.676 | 21.3 | 69 % | 23 | 24 | 26 |
| M24×2 | 2 | 22.0 | 77 % | 21.835 – 22.210 | 23.1 | 66 % | 25 | 26 | 28 |
| M30×2 | 2 | 28.0 | 77 % | 27.835 – 28.210 | 29.1 | 66 % | 31 | 33 | 35 |
UNC – Unified coarse
| Thread | TPI | Cutting tap · 77 % | Forming tap · 65 % | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Drill | in | mm | Thread % | Minor Ø mm (≈2B) | Drill | in | Thread % | ||
| #2-56 | 56 | #50 | 0.0700 | 1.78 | 69 % | 1.693 – 1.818 | 5/64 | 0.0781 | 65 % |
| #4-40 | 40 | #44 | 0.0860 | 2.18 | 80 % | 2.157 – 2.317 | #38 | 0.1015 | 62 % |
| #6-32 | 32 | #36 | 0.1065 | 2.71 | 78 % | 2.646 – 2.846 | 1/8 | 0.1250 | 61 % |
| #8-32 | 32 | #29 | 0.1360 | 3.45 | 69 % | 3.306 – 3.506 | #25 | 0.1495 | 68 % |
| #10-24 | 24 | #25 | 0.1495 | 3.80 | 75 % | 3.680 – 3.916 | 11/64 | 0.1719 | 64 % |
| 1/4-20 | 20 | #8 | 0.1990 | 5.05 | 79 % | 4.975 – 5.240 | #1 | 0.2280 | 65 % |
| 5/16-18 | 18 | F | 0.2570 | 6.53 | 77 % | 6.410 – 6.710 | L | 0.2900 | 60 % |
| 3/8-16 | 16 | 5/16 | 0.3125 | 7.94 | 77 % | 7.807 – 8.107 | S | 0.3480 | 64 % |
| 7/16-14 | 14 | U | 0.3680 | 9.35 | 75 % | 9.149 – 9.484 | 13/32 | 0.4063 | 64 % |
| 1/2-13 | 13 | 27/64 | 0.4219 | 10.72 | 78 % | 10.585 – 10.960 | 15/32 | 0.4688 | 60 % |
| 9/16-12 | 12 | 31/64 | 0.4844 | 12.30 | 72 % | 11.996 – 12.371 | 17/32 | 0.5313 | 55 % |
| 5/8-11 | 11 | 17/32 | 0.5313 | 13.49 | 79 % | 13.375 – 13.825 | 37/64 | 0.5781 | 76 % |
| 3/4-10 | 10 | 21/32 | 0.6563 | 16.67 | 72 % | 16.300 – 16.750 | 45/64 | 0.7031 | 69 % |
| 7/8-9 | 9 | 49/64 | 0.7656 | 19.45 | 76 % | 19.170 – 19.670 | 53/64 | 0.8281 | 62 % |
| 1-8 | 8 | 7/8 | 0.8750 | 22.22 | 77 % | 21.963 – 22.463 | 15/16 | 0.9375 | 74 % |
UNF – Unified fine
| Thread | TPI | Cutting tap · 77 % | Forming tap · 65 % | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Drill | in | mm | Thread % | Minor Ø mm (≈2B) | Drill | in | Thread % | ||
| #4-48 | 48 | #42 | 0.0935 | 2.37 | 68 % | 2.272 – 2.412 | #37 | 0.1040 | 56 % |
| #6-40 | 40 | #33 | 0.1130 | 2.87 | 77 % | 2.818 – 2.978 | #30 | 0.1285 | 56 % |
| #8-36 | 36 | #29 | 0.1360 | 3.45 | 78 % | 3.402 – 3.582 | #24 | 0.1520 | 64 % |
| #10-32 | 32 | #21 | 0.1590 | 4.04 | 76 % | 3.967 – 4.167 | #16 | 0.1770 | 61 % |
| 1/4-28 | 28 | #3 | 0.2130 | 5.41 | 80 % | 5.368 – 5.604 | 15/64 | 0.2344 | 64 % |
| 5/16-24 | 24 | I | 0.2720 | 6.91 | 75 % | 6.792 – 7.028 | M | 0.2950 | 62 % |
| 3/8-24 | 24 | Q | 0.3320 | 8.43 | 79 % | 8.379 – 8.615 | T | 0.3580 | 60 % |
| 7/16-20 | 20 | W | 0.3860 | 9.80 | 79 % | 9.738 – 10.003 | Z | 0.4130 | 72 % |
| 1/2-20 | 20 | 29/64 | 0.4531 | 11.51 | 72 % | 11.325 – 11.590 | 31/64 | 0.4844 | 46 % |
| 9/16-18 | 18 | 1/2 | 0.5000 | 12.70 | 87 % | 12.760 – 13.060 | 17/32 | 0.5313 | 83 % |
| 5/8-18 | 18 | 9/16 | 0.5625 | 14.29 | 87 % | 14.347 – 14.647 | 19/32 | 0.5938 | 83 % |
| 3/4-16 | 16 | 11/16 | 0.6875 | 17.46 | 77 % | 17.332 – 17.632 | 23/32 | 0.7188 | 74 % |
| 7/8-14 | 14 | 51/64 | 0.7969 | 20.24 | 84 % | 20.261 – 20.596 | 27/32 | 0.8438 | 64 % |
| 1-12 | 12 | 59/64 | 0.9219 | 23.42 | 72 % | 23.109 – 23.484 | 31/32 | 0.9688 | 55 % |
Assumptions and sources
- Cutting taps: drill for 77 % of the basic thread depth (1.299 × P), the calculator's default for steel. Metric drills follow ISO 2306 where that drill lies inside the 6H band; otherwise the nearest 0.1 mm drill (0.05 mm below 3 mm) inside the band is used.
- Forming taps: d = D − 0.68 × P × 65 %, nearest drill within ±0.05 mm. This is a rule of thumb – check the tap maker's recommendation.
- Minor diameter: D1 min = D − 1.0825 × P, D1 max = D1 min + TD1 (tolerance 6H, ISO 965-1). For UNC and UNF the same band is used as an approximation of class 2B (ASME B1.1).
- Inch drills: number, letter and fractional (1/64") drills; the one nearest the ideal size inside the band is chosen, so it may differ from older charts by one drill size.
- Clearance holes: ISO 273 fine, medium and coarse series (close, normal and loose fit). ISO 273 covers metric screws only; for inch screws see ASME B18.2.8.
- Generated from the same code as the calculator: Tap Drill Size Calculator · TorqueMath v2.10 · How this calculator was checked
Need a size or setting that is not in the chart?The calculator takes any thread percentage, cutting or forming taps, your material and thread length, and gives the blind-hole depth and tapping speed.
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