Work out a GCD or LCM

Reduce fractions and find when repeating cycles coincide — the two jobs GCD and LCM solve.

Tools used in this guide

The job

GCD is the largest number dividing everything evenly — it reduces fractions and ratios to lowest terms, and answers “the biggest unit that fits all”. LCM is the smallest number all inputs divide — it answers “when cycles meet again” and gives a common denominator.

How to do it

Enter integers separated by spaces or commas — two or more. Read GCD and LCM together; for two numbers they obey LCM = (a × b) ÷ GCD, which is a quick sanity check.

Worked example

Tiling a 12-by-18 area with the biggest square that fits: GCD(12, 18) = 6, so 6-unit squares, six of them. Two buses leave every 12 and every 18 minutes: they leave together every LCM(12, 18) = 36 minutes.

Limits

Integers only — decimals and fractions are rejected. Up to 20 numbers, each within 10¹⁵. LCMs explode combinatorially, so results beyond 10²⁴ are reported as too large rather than as a wrong-looking rounded number.