FractionReference

Nearest fraction

One measurement, every rule: the closest mark in 16ths, 32nds, 64ths and 128ths, so you can trade simplicity against error with the numbers in front of you.

Try:

Presets are conveniences, not standards: they pick which denominators count as “usable.” School stops at twelfths; machining runs to 128ths.

Common questions

What is 0.3937 inches as a fraction?
It depends on the rule. On 16ths the nearest mark is 3/8″; on 32nds it is 13/32″; on 64ths it is 25/64″, which is 0.0006″ oversize. This page answers per rule, with the error of each.
Which rounding rule is used when a value sits exactly between two marks?
Half rounds away from zero — the tape-measure habit. It is documented on the methodology page and pinned by tests, so the same input always gives the same mark.
Can I use metric input here?
Yes — 10 mm works as well as 0.3937 in. Metric input is converted at exactly 25.4 mm per inch and matched the same way.
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.