How to calculate lcm & gcf
GCF via Euclid's algorithm · LCM = a × b ÷ GCF
Worked example. Greatest common factor: 6.
Example inputs — First number: 12; Second number: 18. Starting values are illustrative.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
The GCF is the largest number that divides both numbers evenly. The LCM is the smallest number both divide into. They're linked: LCM = a × b ÷ GCF.
Assumptions & limitations
- Results are rounded for display.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
What's GCF used for?
Simplifying fractions: divide the top and bottom by their GCF.
What's LCM used for?
Finding a common denominator when adding fractions.