FractionReference

Compare two measurements

Inches against millimetres without the unit-conversion coin toss: both values in both units, the exact difference, and which is larger.

Common questions

Is 5/16 inch bigger than 8 mm?
No. 5/16″ is exactly 7.9375 mm, so 8 mm is larger by 0.0625 mm — one sixteenth of a millimetre. This page settles any such pair exactly, in both units.
Why do both sides need units?
Because a bare 8 could be inches or millimetres, and guessing wrong by a factor of 25.4 is the classic shop mistake. Write 8 mm or 8", and nothing is assumed.
How exact is the comparison?
Exact. Both values become rational millimetres via 25.4 mm per inch — a definition, not an approximation — and the difference is computed as a fraction before any display rounding.
Where this comes from. Exact rational arithmetic on the values shown — fractions are pairs of integers until display, and inch–metric conversion uses 25.4 mm to the inch, exact by definition since 1959. See the full methodology.