Decimal & Fraction Converter

How the nearest fraction is chosen

This checks every standard machinist fraction with a denominator of 2, 4, 8, 16, 32, and 64 and picks whichever one lands closest to your decimal — the same set of fractions stamped on a standard fractional drill index or tape measure. It won't suggest an unusual denominator like 1/48 that doesn't actually exist on real tooling, even if it happened to be mathematically closer.

When the rounding actually matters

A decimal that lands almost exactly between two 64ths (say, 0.377 sitting between 3/8 = 0.375 and 25/64 = 0.3906) will round to whichever is numerically closer, but that's a real 0.002 in difference in a dimension — close enough to ignore for a rough clearance hole, and not close enough to ignore for a location that needs to be held tighter. Treat the fraction this gives you as a reading convenience, and go back to the decimal value for anything with a tolerance tighter than about ±0.005 in.