Bolt Size Converter
Convert metric bolt size to imperial inch and common thread pitch.
Result will appear here.
How to use
- Enter a value or select an option.
- Choose the From and To units — the result updates live.
- Also see the converted values in all units below.
Note: metric and imperial bolts are not interchangeable — even if the diameter is close, the thread pitch is different, so do not force them in.
Frequently Asked Questions (FAQ)
What does the bolt size converter do?
It converts a metric bolt size in millimetres to the matching imperial inch size and common thread pitch.
Which metric sizes are covered?
M3, M4, M5, M6, M8, M10, M12, M14, M16, M18 and M20.
What thread pitch information does it show?
Along with the matching inch size, it shows the common thread pitch so you can check the threads match before buying.
Can I use a metric bolt in an imperial thread if the diameter is close?
No. Metric and imperial bolts are not interchangeable because the thread pitch differs, so do not force them in.