Find the greatest common factor
The GCF is the largest positive integer that divides every number without a remainder. For 12, 18, and 24, the GCF is 6. It is also called the greatest common divisor, or GCD.
GCF & LCM Calculator
Find the largest factor your numbers share and the smallest multiple they share. Useful for simplifying fractions and finding common denominators.
GCF & LCM Calculator
Free · No signupUNDERSTAND YOUR ANSWER
How to use this calculator
Find the least common multiple
The LCM is the smallest positive multiple shared by positive input numbers. For 12, 18, and 24, it is 72. For two positive numbers, LCM(a, b) = a × b ÷ GCF(a, b); the tool applies the relationship across your list.
Simplify a fraction or align denominators
The GCF of 12 and 18 is 6, so 12/18 reduces to 2/3. The LCM of denominators 4 and 6 is 12, which supplies a convenient common denominator for adding fractions.
Understand zero and whole-number inputs
When one input is zero and another is positive, GCF(0, n) = n. This tool follows the algebraic convention that a list containing zero has LCM zero. An all-zero list is rejected because there is no greatest positive common factor. Negative values and decimals are outside this tool’s input rules.
A LITTLE MORE CLARITY
Common questions
Can I enter more than two numbers?
Yes. Separate 2–10 whole numbers with commas. All numbers must be between zero and one million.
Are large results exact?
GCF and LCM are calculated using integer arithmetic. Large LCM values are shown as exact whole numbers, not rounded decimals.
About this tool
Created by Marchelle Cook at Roof & Ratio. These calculations run in your browser; entered values are not uploaded or saved by the calculator. Report a calculation issue with an example so we can review it.
Guide updated October 23, 2026. Displayed decimal results may be rounded; exact fraction and integer results are identified in the answer.