LCM Calculator
Find the Least Common Multiple using LCM = |a×b| / GCD(a,b).
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Quick Tip
Enter the two whole numbers.
About This Tool
Why use LCM Calculator?
The least common multiple is the smallest positive number that both of your values divide into exactly. This calculator uses the reliable shortcut LCM(a, b) = |a × b| ÷ GCD(a, b), and shows the GCD, the raw product and the first common multiples so you can see the pattern.
For 4 and 6: the product is 24 and the GCD is 2, so the LCM is 12. Listing multiples confirms it — 4, 8, 12 and 6, 12 — with 12 the first value they share. Multiplying the two numbers always gives a common multiple, but it is only the least one when the numbers are coprime.
Key Benefits
Uses the GCD shortcut
Dividing the product by the GCD is far faster than listing multiples, and works for large numbers.
Common multiples listed
Seeing the first few shared multiples makes the answer easy to verify.
Product shown for comparison
The difference between a × b and the LCM tells you how much the two numbers have in common.
How to use LCM Calculator
- 1
Enter the two whole numbers.
- 2
Read the LCM, and use the listed common multiples to check it by eye.
- 3
Compare the product with the LCM: they match only when the GCD is 1.
- 4
For three or more numbers, take the LCM of the first pair and then combine it with the next number.
Best use cases
Find the common denominator when adding fractions.
Work out when two repeating schedules line up again.
Plan packaging where items come in different pack sizes.
Solve LCM questions in school arithmetic and number theory.
LCM Calculator FAQs
What is the formula for the LCM?
LCM(a, b) = |a × b| ÷ GCD(a, b). For 15 and 20: 300 ÷ 5 = 60.
When is the LCM simply the two numbers multiplied?
When the numbers are coprime, meaning their GCD is 1. For 7 and 9 the LCM is 63, which is exactly 7 × 9.
How is the LCM used with fractions?
The LCM of the denominators is the least common denominator. To add 1/4 and 1/6, rewrite both over 12: 3/12 + 2/12 = 5/12.
What is the LCM of a number and itself?
The number itself, because it is already a multiple of itself and nothing smaller qualifies.
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