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Inch ↔ millimetre
Drill bit
converter.
Turn fractions into millimetres—or go the other way—and grab the closest standard bit the first time.
Size on the plan
IN
Try a fraction like 5/32, a mixed number, or a decimal.
Pick this bitClosest 0.5 mm bit
5/32 in→3.9688 mm exact
The recommended standard size is 0.031 mm away from the exact conversion.
01
Exact conversion.
One inch is exactly 25.4 millimetres. The exact value is shown so you can check tolerances before drilling.
02
Closest bit.
Metric recommendations use 0.5 mm steps. Imperial recommendations use common 1/64-inch increments.
A quick guide
How to use this drill bit size converter
- Enter a measurement in millimetres, decimal inches, or a common fraction.
- Read the matching measurement in the other unit.
- Use the nearest standard fractional-inch bit as a practical reference.
Common questions
Good to know
How do I convert drill bit sizes from inches to millimetres?
Multiply the inch measurement by 25.4. This converter does the calculation and shows the nearest common bit size.
Is a fractional-inch bit always an exact metric match?
Not always. The converter identifies the closest standard fractional-inch size when an exact match is unavailable.