Mathematics Magazine for Grades 1-12  

The Greatest Common Factor and the Least Common Multiplier Calculator

First Number: Second Number:
Third Number (not required):

Greatest Common Factor (GCF):
Least Common Multiplier (LCM):

The greatest common factor

The greatest common factor, or GCF, is the greatest factor that divides two numbers. To find the GCF of two numbers:

  1. List the prime factors of each number.
  2. Multiply those factors both numbers have in common. If there are no common prime factors, the GCF is 1.

The Least Common Multiple

A common multiple is a number that is a multiple of two or more numbers. The common multiples of 3 and 4 are 0, 12, 24, ....

The least common multiple (LCM) of two numbers is the smallest number (not zero) that is a multiple of both.