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LCM calculator

Find the least common multiple (and GCD) of two numbers.

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Enter Number A, Number B and the LCM calculator works out LCM, GCD straight away. For instance, with Number A = 4 and Number B = 6 it returns LCM = 12 and GCD = 2.

How to use it

  1. Enter your values: Number A, Number B.
  2. Read the result instantly: LCM, GCD.

Frequently asked questions

What does the LCM calculator actually compute?

It takes Number A and Number B and derives LCM and GCD from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

2 values: Number A and Number B. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Number A = 4 and Number B = 6, the calculator returns LCM = 12 and GCD = 2. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Number A = 8 and Number B = 12 instead, LCM goes from 12 to 24 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Number A = 2 and Number B = 3, LCM comes out at 6. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Reading a number written another way: a Roman numeral on a monument, a hexadecimal colour, a binary byte, or a fraction that needs reducing.

What is the most common mistake?

Assuming a decimal fraction survives a change of base. A tenth is exact in decimal and infinitely repeating in binary, which is why 0.1 + 0.2 is not 0.3 in most programming languages.

Where do the figures come from, and how current are they?

Base conversion and number-theory results are exact. Roman numerals follow the standard subtractive form used since the Middle Ages, which is not the only one the Romans themselves used.

Further reading

All guides →
How-toLCM and GCD ExplainedThe GCD is the biggest shared divisor; the LCM is the smallest shared multiple. Here's what each means, how to find them with prime factors, and the shortcut linking them.How-toHow to Simplify a RatioDivide both sides by their greatest common divisor. Here's what a ratio is, how to reduce it, why units must match first, and how to compare ratios.ExplainerSignificant Figures Explained: Counting, Rounding, and Why They MatterLearn what counts as a significant figure, the rules for leading, trailing, and captive zeros, and how sig figs keep your calculated answers honest.How-toHow to Find Prime Factors: Factor Trees and the Division MethodBreak any whole number into its prime building blocks with a factor tree or repeated division — and write the result as a clean prime factorization with exponents.How-toHow to Multiply and Divide Fractions: Multiply Across, Flip to DivideMultiplying fractions needs no common denominator — just multiply across. Dividing means multiplying by the reciprocal. Learn both with worked examples and how to simplify.How-toHow to Convert a Fraction to a DecimalDivide the top number by the bottom. Here's the rule, why some fractions repeat, how to round them, and how to turn the result into a percentage.