Drill Bit Size Converter
Convert any drill bit size between millimetres, decimal inches, inch fractions, number gauges and letter sizes: enter the size in mm and instantly see every equivalent, including the nearest gauge and letter match.
Result will appear here.
How to use
- Type the drill size in millimetres in the input box.
- The page updates live: see the size as decimal inches, the nearest 64th-inch fraction, and the nearest gauge number and letter size.
- Remember gauge and letter values are the nearest match — check the actual bit before drilling.
Note: In number gauges, a bigger number = smaller drill. Letter sizes run from A to Z.
Frequently Asked Questions (FAQ)
What units can I convert between?
Drill bit sizes convert between millimeters, decimal inches, inch fractions, gauge numbers, and letter sizes.
How do number gauges work?
In number gauges, a bigger number means a smaller drill. Letter sizes run from A to Z.
Does the result update as I type?
Yes. Pick the From and To units and the converted values in all units appear right away.
Are the gauge and letter values exact?
No. They are the nearest match to your size, so check the actual bit before drilling.