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Least Common Multiple Calculator

Find the least common multiple (LCM) of two or more whole numbers. The result comes with the prime factorisation of each number and the greatest common factor.

Formulas last reviewed: September 2026

Disclaimer: Results are calculated with standard formulas and are meant for learning and quick checks. Please double-check important work, especially anything used for exams, engineering, finance or safety.

The smallest number they all divide into

The least common multiple (LCM) of two or more whole numbers is the smallest positive number that every one of them divides evenly. It is what you need to add or subtract fractions with different denominators and to find when repeating events line up.

This calculator finds the LCM of up to ten numbers, and shows their prime factorisations and the greatest common factor as well.

How it is calculated

Prime-factor each number
Take every prime at its highest power
Multiply them together
For two numbers: LCM × GCF = a × b

Worked example

LCM of 12, 18 and 30

12
2^2 × 3
18
2 × 3^2
30
2 × 3 × 5
LCM
180

Where the LCM is useful

  • Adding fractions: 1/12 + 1/18 uses 36 as the common denominator.
  • Scheduling: buses that run every 12 and 18 minutes leave together every 36 minutes.
  • Gears and tiling problems where repeating patterns must match.

Frequently asked questions

What is the LCM of two prime numbers?

It is simply their product. The LCM of 5 and 7 is 35.

How are LCM and GCF related?

For two numbers, LCM × GCF equals the product of the numbers. Knowing one lets you find the other quickly.

Can I find the LCM of more than two numbers?

Yes, enter up to ten whole numbers separated by commas or spaces.

Is the LCM ever smaller than the numbers?

No. The LCM is always at least as large as the biggest number in the list.