Drill Bit Size Converter

Quick answer

Drill bit sizes are expressed as numbers, letters, fractional inches, or millimeters depending on region.

Matching the correct letter or number bit matters when charts call out inch pilot diameters.

Use the converter below, then apply tap drill size guidance when you prepare holes for tapping.

Convert drill bit sizes between number, letter, inch, and millimeter systems.

Tie results to tap drill size picks when you match pilot bits to taps.

Use screw size conversion when you mix metric and inch stocked sets.