Highest common factor of 30 and 12

Highest common factor (or GCF: greatest common factor) of 12 and 30 is: 6

Factors of 12: 1, 2, 3, 4, 6, 12
Factors of 30: 1, 2, 3, 5, 6, 10, 15, 30

To find the greatest common factor, look through the listed factors of both 12 and 30 and pick out the common factors. The common factors of 12 and 30 are 1, 2, 3, and 6. Which number out of the common factors is the greatest? 6 is the greatest, making it the greatest (highest) common factor.