AbraCalc

Drill Bit Size Converter

Convert fractional inch drill bit sizes to millimetres. Covers 1/16" through 1/2".

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How to use this tool

  1. Enter drill bit size in the fields above.
  2. Results update instantly as you type — or click Calculate.
  3. Read your diameter and the full breakdown beneath it.

Convert fractional inch drill bit sizes to metric (mm) equivalents for any drilling project.

Frequently asked questions

What is a 1/4 inch drill bit in mm?
A 1/4" drill bit is 6.35 mm in diameter. To convert any fraction to mm, multiply the decimal value by 25.4.

References & sources