The largest number dividing two or more numbers into the same number is called the GCM , or the largest common divisor, GCD , when the common divisors of these numbers are the largest. The largest common divisor of natural numbers a and b is denoted GCD (a, b) or (a, b) GCD. How can you use GCD calculator ? It’s so easy. Firstly, we write two numbers side by side to make a divisor list. Then we start from the smallest prime number. If the two numbers are not divided, we are look at large prime number. Processing continues until both numbers are 1. However, the important thing here is that we need to mark the divisor numbers for both numbers. For example, the common prime factors 18, 24 and 30 are the common prime factors 2 and 3. By multiplying by 2 and 3, there are 2x3 = 6 numbers. So the number 6 is the largest number that can divide the numbers 18, 24 and 30.