Least Common Multiple Calculator guide
Least Common Multiple Calculator: Find the LCM
Use our least common multiple calculator to find the LCM of two or more whole numbers, with prime factorisation working.
By the AllCalculator editorial teamUpdated 16 October 20261 min read
The least common multiple (LCM), also called the lowest common multiple, is the smallest number that two or more numbers all divide into. Our Least Common Multiple Calculator finds it for any list of numbers.
How to use the calculator (Least Common Multiple Calculator)
Type two or more whole numbers, separated by commas or spaces. You'll see the LCM, the greatest common factor and each number's prime factorisation.
How to find the LCM
Using prime factors: write each number as a product of primes, then multiply each prime at its highest power.
Using the GCF: for two numbers, LCM(a, b) = a × b ÷ GCF(a, b).
A worked example
With the calculator's default settings, 4, 6 and 15:
- 4 = 2²
- 6 = 2 × 3
- 15 = 3 × 5
- LCM = 2² × 3 × 5 = 60
Frequently asked questions
What's the LCM used for?
Adding and subtracting fractions (it gives the lowest common denominator), and working out when repeating events line up, such as buses that leave every 12 and 18 minutes (every 36 minutes).
What's the difference between the LCM and the GCF?
The LCM is the smallest number they all go into. The GCF is the biggest number that goes into all of them.
Can the LCM be one of the numbers?
Yes. The LCM of 4 and 12 is 12.
For the greatest common factor, use our Greatest Common Factor Calculator.
Sources and further reading
- GOV.UK: National curriculum in England – mathematicsgov.uk
- Wolfram MathWorld: Least common multiplemathworld.wolfram.com
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.