GCD & LCM Calculator
Enter two or more numbers separated by commas to find their greatest common divisor and least common multiple.
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How to find the GCD and LCM
- Type two or more whole numbers separated by commas, for example
12, 18, 30. - Read the greatest common divisor (GCD, also called HCF) and the least common multiple (LCM).
What these mean
GCD (greatest common divisor) is the largest number that divides evenly into all the given numbers — useful for simplifying fractions. LCM (least common multiple) is the smallest number that all the given numbers divide into evenly — useful for finding common denominators or syncing repeating cycles.
Questions about GCD, HCF and LCM
Is the GCD the same as the HCF?
Yes. Greatest common divisor (GCD), highest common factor (HCF) and greatest common factor (GCF) are three names for the same thing.
How do I find the HCF of two numbers?
List the factors of each and pick the largest they share. Factors of 12 are 1, 2, 3, 4, 6, 12 and of 18 are 1, 2, 3, 6, 9, 18, so the HCF is 6.
How do I find the LCM of two numbers?
Multiply them and divide by their GCD. For 4 and 6: 4 × 6 ÷ 2 = 12.
What are they used for?
The GCD simplifies fractions and ratios. The LCM finds a common denominator for adding fractions, or when two repeating events next line up, such as buses every 12 and 18 minutes meeting every 36 minutes.