This greatest common factor calculator will find for you the greatest factor two numbers have in common.

Enter your first number into the box on top.

Enter your second number into the box in the middle.

Hit calculate et voilà! Recall that the factor of a number is any number that divides the number evenly.

For example factors for 10 are 1, 2, 5, and 10

Factors of 20 are 1, 2, 4, 5, 10, and 20

As you can see common factors for 10 and 20 are 1, 2, 5, and 10. However, the greatest one is 10, so 10 is the greatest common factor.