How to use the LCM Calculator
Enter two or more whole numbers separated by commas or spaces. The result is the smallest number that all of them divide into evenly.
Worked example
The LCM of 4 and 6 is 12: the multiples of 4 are 4, 8, 12 and those of 6 are 6, 12, so 12 is the first they share. For bigger numbers, use LCM(a, b) = a × b ÷ GCD(a, b). For 6 and 8, the GCD is 2, so the LCM is 48 ÷ 2 = 24.
Everyday uses
If one bus comes every 12 minutes and another every 18 minutes, and both leave now, they next leave together after 36 minutes, the LCM of 12 and 18. The LCM is also the lowest common denominator when you add fractions like 1/4 and 1/6.
LCM and GCF together
The least common multiple and the greatest common factor are two sides of the same idea. The LCM is the smallest positive number that every input divides into, while the greatest common factor, also called the greatest common divisor, is the largest number that divides into every input. For 8 and 12, the GCF is 4 and the LCM is 24, and 4 × 24 = 96 = 8 × 12. If you need the GCF, use the GCF calculator.
The formula
LCM(a, b) = a × b ÷ GCD(a, b)
Examples
- LCM of 12, 18 and 30
LCM(12, 18, 30) = 180
- LCM of 4 and 6
LCM(4, 6) = 12
- LCM of 7, 9 and 21
LCM(7, 9, 21) = 63
Limitations and assumptions
Computed in your browser with standard double-precision arithmetic unless the page says otherwise. Very large or very small values may be rounded.
Frequently asked questions
How do you find the LCM?
List the prime factorisation of each number and take the highest power of every prime that appears. Multiply those together.
What is the relationship between LCM and GCD?
For two numbers, LCM times GCD equals the product of the numbers, so LCM(a, b) = a × b ÷ GCD(a, b).
When do I use the LCM?
To find a common denominator for adding fractions, or to find when two repeating events (every 4 days and every 6 days) coincide.
Can I enter more than two numbers?
Yes. Separate numbers with commas or spaces.