Greatest common factor (GCF) calculator. Is also known as greateset common divisor (GCD).

The greatest common factor (GCF or GCD or HCF) of a set of whole numbers is the largest positive integer that divides evenly into all numbers with zero remainder. For example, for the set of numbers 18, 30 and 42 the GCF = 6.

Find GCF for numbers 8 and 12:

The divisors of 8 are:

8 = 2×2×2

The divisors of 12 are:

12 = 2×2×3

So the common divisors of 8 and 12 are:

gcf = 2×2 = 4

So 8/12 fraction, can be reduced to 2/3:

8 / 12 = (8/4) / (12/4) = 2 / 3