LCM calculator
The least common multiple (LCM) of two or more numbers.
About this calculator
This LCM calculator finds the least common multiple of a list of whole numbers: the smallest number they all divide into exactly.
It's the lowest common denominator you need when adding or subtracting fractions.
How it works
For two numbers, LCM = a × b ÷ GCF(a, b). For more numbers, the calculator takes the LCM of the first two, then of that result and the next number, and so on.
Last reviewed:
Worked example
- Whole numbers, separated by spaces or commas: 4, 6, 15
Least common multiple: 60
Common questions
How do I find the LCM of two numbers?
Multiply them and divide by their GCF. For 4 and 6, 4 × 6 ÷ 2 = 12.
What is the LCM used for?
Adding fractions with different denominators, and timing problems, such as when two buses on different schedules next leave together.
What is the difference between LCM and GCF?
The GCF is the largest number that divides into all of them, and the LCM is the smallest number they all divide into.
The story behind it
Where the idea came from: Adding fractions has always needed a common denominator, the least common multiple of the bottom numbers.
Ancient Egyptian scribes worked with unit fractions such as 1/2 and 1/3, and finding common multiples was part of everyday sums. The idea is the same in a classroom today.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
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