Tap Drill Size Calculator
Drill size for any metric or unified thread at chosen % engagement.
M10×1.5 → 8.5 mm drill: the D−P rule. 75% thread carries ~95% of full strength but taps with HALF the torque — 100% threads mostly produce broken taps.
Formula
Tap Drill Size Calculator is a free tap drill size for mechanical and machine-design engineers — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Tap Drill Size Calculator
Drill size for any metric or unified thread at chosen % engagement. The calculation implements drill = D − P×(%/77); at 77%: simply D − P (Machinery's Handbook — tapping). M10×1.5 → 8.5 mm drill: the D−P rule. 75% thread carries ~95% of full strength but taps with HALF the torque — 100% threads mostly produce broken taps.
How to use Tap Drill Size Calculator
- 1Enter Thread major diameter in mm.
- 2Enter Thread pitch in mm (M6×1 · M8×1.25 · M10×1.5 · M12×1.75).
- 3Enter Thread engagement in %.
- 4Read Tap drill diameter instantly — no submit button needed.
- 5Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Tap Drill Size Calculator?
- ✓Implements the standard formula — drill = D − P×(%/77); at 77%: simply D − P
- ✓Reference cited on-page: Machinery's Handbook — tapping
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Tap Drill Size Calculator use?+
It computes drill = D − P×(%/77); at 77%: simply D − P, per Machinery's Handbook — tapping. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
M10×1.5 → 8.5 mm drill: the D−P rule. 75% thread carries ~95% of full strength but taps with HALF the torque — 100% threads mostly produce broken taps.
Is this suitable for machine design coursework?+
Yes — these are the exact Shigley/Machinery's-Handbook formulas, with the substitution shown step by step, so you can follow the worked example into your own calculation sheet.
Is the Tap Drill Size Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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