Tap Drill Calculator & Chart
Need mm to inch drill bit conversions? Visit Drill Bit Size Conversion.
Tap Drill Calculator
Compute recommended tap drill using an engagement slider. Formula: drill = major − (1.082 × pitch × engagement). For imperial, pitch = 1 ÷ TPI.
Nearest Standard Bit Mapping
For critical fits, consult manufacturer charts. Engagement slider uses 60° V-thread geometry with factor 1.082; actual fit depends on tap class and hole quality.
Tap Drill Chart (UNC/UNF & Metric)
Common thread combinations and recommended drills. Adjust per manufacturer guidance and material.
Open thread conversion| Thread | Recommended Drill | Inches | mm |
|---|---|---|---|
| #6-32 UNC | #36 | 0.1065" | 2.705 mm |
| #8-32 UNC | #29 | 0.1360" | 3.454 mm |
| #10-24 UNC | #25 | 0.1495" | 3.797 mm |
| #10-32 UNF | #21 | 0.1590" | 4.039 mm |
| 1/4-20 UNC | #7 | 0.2010" | 5.105 mm |
| 5/16-18 UNC | F | 0.2570" | 6.528 mm |
| 3/8-16 UNC | 5/16" | 0.3125" | 7.938 mm |
| M3×0.5 | 2.5 mm | 0.0984" | 2.499 mm |
| M4×0.7 | 3.3 mm | 0.1299" | 3.299 mm |
| M5×0.8 | 4.2 mm | 0.1654" | 4.201 mm |
| M6×1.0 | 5.0 mm | 0.1969" | 5.001 mm |
| M8×1.25 | 6.8 mm | 0.2677" | 6.8 mm |
| #4-40 UNC | #43 | 0.0890" | 2.261 mm |
| #6-40 UNF | #33 | 0.1130" | 2.87 mm |
| #8-36 UNF | #28 | 0.1405" | 3.569 mm |
| 1/4-28 UNF | #3 | 0.2130" | 5.41 mm |
| 5/16-24 UNF | I | 0.2720" | 6.909 mm |
| 3/8-24 UNF | Q | 0.3320" | 8.433 mm |
| 7/16-14 UNC | 23/64 | 0.3594" | 9.129 mm |
| 7/16-20 UNF | U | 0.3680" | 9.347 mm |
| 1/2-13 UNC | 27/64 | 0.4219" | 10.716 mm |
| 1/2-20 UNF | 29/64 | 0.4531" | 11.509 mm |
| M2×0.4 | 1.6 mm | 0.0630" | 1.6 mm |
| M10×1.5 | 8.5 mm | 0.3346" | 8.499 mm |
| M12×1.75 | 10.2 mm | 0.4016" | 10.201 mm |
| M3×0.35 (fine) | 2.65 mm | 0.1043" | 2.649 mm |
| M4×0.5 (fine) | 3.5 mm | 0.1378" | 3.5 mm |
| M5×0.5 (fine) | 4.5 mm | 0.1772" | 4.501 mm |
| M6×0.75 (fine) | 5.2 mm | 0.2047" | 5.199 mm |
| M8×1.0 (fine) | 7.0 mm | 0.2756" | 7 mm |
| M10×1.25 (fine) | 8.8 mm | 0.3465" | 8.801 mm |
| M12×1.5 (fine) | 10.5 mm | 0.4134" | 10.5 mm |
| M14×1.0 (fine) | 13.0 mm | 0.5118" | 13 mm |
| M16×1.5 (fine) | 14.5 mm | 0.5709" | 14.501 mm |
| M20×1.5 (fine) | 18.5 mm | 0.7283" | 18.499 mm |
| M18×1.0 (fine) | 17.0 mm | 0.6693" | 17 mm |
| M22×1.5 (fine) | 20.5 mm | 0.8068" | 20.493 mm |
Note: Manufacturer and material recommendations may vary. For high precision, consult official charts or test on scrap.
ISO tolerance note: Metric threads commonly use classes like 6H (internal) and 6g (external). Tap drill sizes are approximate; final fit depends on ISO 261/965 tolerances, tap class, and hole quality.