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Least Common Multiple Calculator

LCM by prime factorisation, listing and the GCF shortcut.

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Separate with commas or spaces. Two or more whole numbers.

Method 1 — prime factorisation

Take every prime that appears, raised to the highest power it reaches.

NumberPrime factorisation

Method 2 — listing multiples

The first value that appears in every row is the LCM.

NumberMultiples

Method 3 — the GCF shortcut

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Least common multiple

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Related values

Greatest common factor—
Numbers given—
LCM ÷ each number—
Next common multiple—

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Least common denominator for these values

The LCM rule mirrors the GCF rule: shared primes at their lowest power give the GCF, all primes at their highest power give the LCM. For two numbers, GCF × LCM equals their product. Adding fractions is the usual reason people need this, since the least common denominator is the LCM of the denominators.

Quick Tool Overview

The Least Common Multiple Calculator finds the smallest number every one of your numbers divides into, using prime factorisation, the GCF shortcut and a listed multiples table so you can see all three routes to the same answer.

What it does
Finds the LCM of two or more numbers, three ways
You give it
Two or more whole numbers
You get back
The LCM plus factorisation, shortcut and a table
Best for
Adding fractions and scheduling-style problems
Calculators Free, unlimited use No sign-up Runs in your browser

About the Least Common Multiple Calculator

Find the smallest number that every one of your numbers divides into, worked out three ways: by listing multiples until they meet, by prime factorisation, and by the shortcut that divides the product of two numbers by their greatest common factor.

The factorisation method is the one worth internalising — take every prime that appears in any of the numbers, raised to the highest power it reaches in any of them. That mirrors the GCF rule, which takes shared primes at their lowest power, and the symmetry explains the identity GCF × LCM = a × b for a pair of numbers. Adding fractions is the usual reason people need this, since the least common denominator is exactly the LCM of the denominators.

Key features of the Least Common Multiple Calculator

Three methods compared

Listing multiples, prime factorisation, and dividing the product by the GCF — the fastest route for large numbers.

Multiples table

Multiples of each number listed until they coincide, which is how the concept is usually first taught.

The GCF identity

For two numbers, GCF × LCM equals their product — shown and used rather than just mentioned.

Least common denominator

The page connects the LCM directly to adding fractions, which is why most people need it.

Any number of inputs

Computed across the whole set, not just a pair.

How to use the Least Common Multiple Calculator

  1. 1

    Enter your numbers

    Two or more whole numbers, separated by commas or spaces.

  2. 2

    Read the LCM

    The smallest number all of them divide into exactly.

  3. 3

    Compare the methods

    Prime factorisation, the GCF shortcut, and a table of multiples until they coincide.

  4. 4

    Use it as a denominator

    For adding fractions, the LCM of the denominators is the least common denominator.

Frequently asked questions

The smallest positive number that every number in a set divides into exactly. For 4 and 6 it is 12.

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