What is a GCF?
The greatest common factor (GCF), also called the greatest common divisor (GCD) or highest common factor (HCF), is the largest positive integer that divides every selected number without a remainder.
ExampleFactors of 24: 1, 2, 3, 4, 6, 8, 12, 24
Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36
Greatest common factor = 12
How this calculator works
Choose the view that helps you learn or verify the answer.
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Euclidean algorithm
Repeated division reduces large numbers quickly until the remainder is zero.
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Prime factorization
Prime factors show which building blocks all the numbers share.
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Factor comparison
The visual map highlights every common factor and the greatest one.
How to find the GCF
For small numbers, list every factor and choose the largest one present in all lists. For large numbers, use the Euclidean algorithm: divide the larger number by the smaller, replace the pair with the smaller number and the remainder, and repeat. With more than two numbers, calculate the GCF of the first pair, then combine that result with each remaining number.