LCM Calculator
List your numbers and get the least common multiple straight away. The greatest common factor is shown as well, since the two are linked.
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The formula
LCM(a, b) = (a x b) / GCF(a, b)
What the LCM is
The least common multiple is the smallest number that every number in your list divides into evenly. For 4 and 6, the multiples of 4 are 4, 8, 12, 16 and the multiples of 6 are 6, 12, 18, so the LCM is 12.
Where you use it
The LCM is how you find a common denominator for adding fractions: 1/4 + 1/6 uses 12 as the denominator. It also answers timing puzzles, such as two buses that run every 12 and 18 minutes and leave together at noon. They next leave together after 36 minutes.
Three ways to find it
- Listing multiples: write them out until you find the first match. Fine for small numbers.
- Prime factors: break each number into primes and take the highest power of each. 12 = 2^2 x 3 and 18 = 2 x 3^2, so the LCM is 2^2 x 3^2 = 36.
- The GCF shortcut: multiply the numbers and divide by their GCF. 12 x 18 / 6 = 36.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Whole numbers (separated by commas or spaces): 12 18 | Least common multiple (LCM): 36 |
| Whole numbers (separated by commas or spaces): 4 6 10 | Least common multiple (LCM): 60 |
| Whole numbers (separated by commas or spaces): 24 36 60 | Least common multiple (LCM): 360 |
| Whole numbers (separated by commas or spaces): 7 11 | Least common multiple (LCM): 77 |
LCM Calculator: frequently asked questions
Can I find the LCM of more than two numbers?
Yes. Enter as many as you like (up to 50). The calculator works through them one pair at a time.
What is the LCM of two prime numbers?
Simply their product. The LCM of 7 and 11 is 77.
How accurate is this calculator?
It uses standard double-precision arithmetic, accurate to about 15 significant digits. Results are rounded only for display.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026