How to use this GCF calculator
- Enter two or more positive whole numbers separated by spaces (for example: 54 24 36). Up to 100 numbers, each up to 500 digits.
- Press Calculate — or just press Enter in the field. The Greatest common factor (GCF) field shows the largest number that divides all of your inputs without a remainder.
- The Least common multiple (LCM) field shows the smallest positive number that is a multiple of all of them, with the lcm(…) expression repeated underneath.
- Press Reset to return to the example numbers and clear the results, or Shift+Enter to put each number on its own line.
The greatest common factor (GCF, also called greatest common divisor, GCD) of a set of numbers is the largest positive integer that divides each of them evenly. Find GCF for the numbers 8 and 12: the prime factors of 8 are 2 × 2 × 2 and the prime factors of 12 are 2 × 2 × 3, so the common prime factors give gcf(8, 12) = 2 × 2 = 4 — which is also how you reduce the fraction 8/12 to 2/3 by dividing top and bottom by 4.
The least common multiple (LCM) is the smallest positive number every input divides into evenly: lcm(8, 12) = 24. For the default example 54 24 36 the calculator returns GCF = 6 and LCM = 216. Coprime numbers like 7 and 13 share no factor, so their GCF is 1 and their LCM is their product, 91.
Every result is an exact whole number computed by arbitrary-precision integer arithmetic in your browser — numbers far beyond an ordinary calculator's 2⁵³-precision limit keep all their digits, and nothing is uploaded anywhere. Zeros, negatives, decimals and non-numeric text are rejected with a clear message instead of a result.
More math tools are in Math & Statistics.