Tap Drill Size Lookup — UNC, UNF, NPT & Metric Tool

Tap Drill Size Lookup Tool

Find the correct tap drill size for UNC, UNF, NPT, and Metric threads — for both cutting taps and form (roll) taps. Select your tap type, thread, and get the right drill size instantly.


UNC (Unified National Coarse)
UNF (Unified National Fine)
NPT (National Pipe Taper)
Metric (Coarse Pitch)

How to Use This Tool

  1. Select your tap type — Cutting or Form (Roll). This is critical — they use different drill sizes.
  2. Select the thread standard (UNC, UNF, NPT, or Metric).
  3. Choose the specific thread size from the dropdown list.
  4. The recommended tap drill size and its decimal equivalent will be displayed.

Cutting tap drills target ~75% thread engagement. Form tap drills are larger, targeting ~65% engagement, because the tap displaces material rather than removing it.

⚠️ Don’t Mix Up Your Drill Sizes

Using a form tap drill (larger hole) with a cutting tap produces dangerously shallow threads that can strip under load.

Using a cutting tap drill (smaller hole) with a form tap will likely break the tap — form taps have nowhere to push the extra material.

Not sure which tap type to use? Read our guide: Cutting Taps vs. Form Taps — When to Use Each