Tap Drill Calculator
Quick answer
Tap drill size is the pilot hole diameter you drill before cutting internal threads with a tap.
It is smaller than major diameter so taps form enough thread height without over-torquing.
Use the calculator below for metric sizes, then cross-check inch pilots with tap drill charts when needed.
Bolt sizing and thread specifications follow widely recognized mechanical standards used in engineering and manufacturing. Standard bolt sizing references, industrial fastener charts, and mechanical thread standards ensure compatibility, safety, and correct tool selection across applications.
Pick a metric thread size and optionally adjust pitch; recommended tap drill size updates instantly. See screw anatomy for major diameter and thread types when series labels are unclear.
Calculator
Calculation method
For metric taps, a common workshop formula is major diameter minus pitch. This tool also shows coarse reference values from a lookup table. Cross-check unknown threads with the thread identifier before you tap critical parts.
See full M6 bolt specifications · Spanish: perno M6 · All size reference pages.