Inches to Fraction Calculator

Convert a decimal inch measurement to the nearest fraction — down to 1/8, 1/16, 1/32, or 1/64 — plus its value in millimetres, reduced to lowest terms.

Nearest fraction

3/8"

As decimal (rounded)—

Millimetres—

Rounding error—

How it works

To turn a decimal inch into a fraction, multiply by the denominator (say 16), round to the nearest whole number for the numerator, then reduce the fraction by the greatest common divisor.

numerator = round(decimal × denominator)
fraction = numerator / denominator, then reduce

Worked example

0.375 inches × 16 = 6, so 6/16, which reduces to 3/8" (9.525 mm).

Frequently asked questions

How do I convert a decimal inch to a fraction?

Multiply by 16, round, and reduce. 0.375 → 6/16 → 3/8.

What is 0.25 inches as a fraction?

Exactly 1/4 inch (6.35 mm).