GCF & LCM Calculator
Find the greatest common factor (GCF/HCF) and least common multiple (LCM) of any set of whole numbers — enter two or more numbers separated by commas.
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Save ⟶How to use the GCF & LCM Calculator
- 1Enter numbers (comma separated) in the form on the left.
- 2Fill in the remaining fields — the result updates automatically as you type.
- 3Review the highlighted result and the supporting breakdown on the right.
- 4Use Copy, Share or Print to save or send your result.
GCF and LCM explained
The greatest common factor (also called HCF or GCD) is the largest number that divides all the given numbers evenly — essential for simplifying fractions. The least common multiple is the smallest number that all the given numbers divide into — essential for adding fractions and scheduling repeating events.
They are linked by a neat identity for two numbers: GCF × LCM = a × b. The calculator uses the fast Euclidean algorithm rather than listing factors.
Frequently Asked Questions
▸What is the GCF used for?
Mostly simplifying fractions (divide top and bottom by the GCF) and splitting things into equal largest-possible groups.
▸What is the LCM used for?
Finding common denominators when adding fractions, and answering 'when do two repeating cycles line up?' questions.