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GCF Calculator

Find the greatest common factor and least common multiple of two or more whole numbers, with each number's prime factorization, the full list of factors and a prime check.

Updated November 4, 2026. Free, no sign-up; everything runs in your browser and nothing you type is stored.

GCF calculator and LCM calculator

Whole numbers (2 or more)

Greatest common factor (GCF)

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–Least common multiple (LCM)

–Prime?

Prime factorization

All factors of the first number

How to find the GCF

The greatest common factor (also called the greatest common divisor, GCD, or highest common factor, HCF) is the largest number that divides all of them. Two ways:

Prime factors: 12 = 2² × 3, 18 = 2 × 3², 30 = 2 × 3 × 5. Take each prime that appears in all of them at its lowest power: 2 × 3 = 6.
Euclid's algorithm: GCF(a, b) = GCF(b, a mod b). GCF(48, 18): 48 mod 18 = 12, 18 mod 12 = 6, 12 mod 6 = 0, so 6.

LCM calculator: least common multiple

The least common multiple calculator finds the smallest number that all of them divide into. Take every prime at its highest power: 2² × 3² × 5 = 180 for 12, 18 and 30. For two numbers, LCM(a, b) = a × b ÷ GCF(a, b): LCM(12, 18) = 216 ÷ 6 = 36. The LCM is the least common denominator when adding fractions.

Factoring calculator: prime factorization and factors

Prime factorization writes a number as a product of primes, which is unique for every whole number above 1 (the fundamental theorem of arithmetic): 360 = 2³ × 3² × 5. Multiply one more than each exponent to count all factors: 360 has (3 + 1)(2 + 1)(1 + 1) = 24 factors. To factor a quadratic like x² − 5x + 6, use the quadratic formula calculator.

Common questions

What is the GCF of 12, 18 and 30?

What is the LCM of 12, 18 and 30?

180.

How do I find the LCM of two numbers?

Multiply them and divide by their GCF: LCM(12, 18) = 216 ÷ 6 = 36.

What is the prime factorization of 360?

2³ × 3² × 5.

Is GCF the same as GCD and HCF?

Yes: greatest common factor, greatest common divisor and highest common factor are the same thing.

Sources

General information, not financial, tax or legal advice. Check important numbers with the official source before acting on them.