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Math — Number Theory

LCM Calculator

Enter two numbers to get the least common multiple — and the greatest common factor.

Filed by The Statistics Desk  |  Method: LCM = a × b ÷ GCF
Least common multiple
—
Smallest number both divide.
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Greatest common factor—
First number—
Second number—
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Enter your figures above to see the step-by-step working.
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How the LCM Calculator Works

The least common multiple (LCM) is the smallest positive number that both of your numbers divide into evenly. It is what you need to add or subtract fractions with different denominators — the LCM of the denominators is the least common denominator.

The quickest way to find it is through the greatest common factor: multiply the two numbers and divide by their GCF. This calculator does exactly that and shows the GCF too. Enter two positive whole numbers.

LCM = a × b ÷ GCF(a, b)

Frequently Asked Questions

What is the least common multiple?

It is the smallest number that both of your numbers divide into without a remainder. For 4 and 6 it is 12.

When do I need the LCM?

Most often when adding or subtracting fractions: the least common denominator is the LCM of the denominators. It also appears in scheduling and pattern problems.

How is the LCM related to the GCF?

They multiply to the product of the two numbers: a × b = GCF × LCM. So dividing the product by the GCF gives the LCM, which is how this calculator finds it.

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