Tap Drill Calculator

Tap Drill Calculator gives you tap drill size, percent thread engagement, and clearance holes for inch and metric threads, with the formula shown on screen.

Use this tap drill calculator for Unified (inch) and ISO (metric) threads, using the standard Machinery's Handbook engagement-constant formula, so you can check the math against your own reference before you drill.

TAP DRILL
- Pick a thread from the fractional, number, letter, or metric series
- Choose a percent engagement, including presets for standard and lighter engagement on harder materials
- See the tap drill size and its decimal diameter
- See the closest standard drills above and below your target, each with the actual percent engagement it produces
- Enter a drill size you already have to see the actual percent engagement it gives, in either direction

THREADS
- Search and filter the standard drill and thread table by series
- See each thread's paired tap drill and clearance-hole size for close, normal, and loose fit
- See minimum thread engagement length by material class - steel, cast iron/brass, or aluminum - as a multiplier of nominal diameter
- See the source references behind the table

SAVED
- Save named presets of thread, engagement percent, and drill index
- Keep a history of calculated results
- Load any saved preset or result back into the Tap Drill tab

BUILT FOR THE SHOP FLOOR
- Fast entry with minimal taps
- Works offline
- No account required
- Saved presets and history stay on your device

This app is ad-supported. The calculators are available to use; watching a short ad unlocks saving results, calculation history, and saved presets.

If you need a tap drill size calculator, thread engagement calculator, or clearance hole chart for inch or metric threads, this app gives you the numbers with the formula shown.

Recent changes:
First release.

Pick a Unified or ISO thread and the app gives the tap drill size for the engagement you want, or the percent engagement for a drill you have.

Clearance holes and the formula are shown alongside.