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Greatest Common Factor Calculator

Find the GCF of up to 15 numbers with three methods side by side: the Euclidean algorithm, prime factorisation and factor listing.

Related tools

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Common Factor CalculatorFind every common factor of 2 to 10 numbers, with the greatest common factor highlighted and coprime pairs flagged.Factor CalculatorList every divisor of a whole number in pairs, with the divisor count, the divisor sum, and whether it is prime, perfect, abundant or deficient.Prime Factor CalculatorFactor any integer up to 10^15 with Pollard's rho and Miller-Rabin, with the factor tree, exponent form, divisor count, sigma and Euler's totient.Amicable Number CheckerCheck whether two numbers are amicable — or give just one and get its candidate partner plus the verified loop, with perfect and sociable numbers identified.Arctan2 Calculator (atan2 of y and x)atan2(y, x) is not atan(y/x): it reads the signs of both arguments to place the angle in the right quadrant over the full −180°…180° turn, and it stays defined when x = 0. Enter x and y, read the angle in degrees or radians, see the quadrant and the point plotted. For a single ratio with no quadrant information, use the arctan calculator instead.Divisibility Test CalculatorTest a number against the divisors 2 to 12, the primes up to 100 or your own list — and see the mental rule and the working, not just yes or no.e Digits Calculator (Euler's Number)Compute up to 1,000 decimals of Euler's number e from the series Σ 1/k!, with digit frequencies, a digit search and the 1828 1828 trap explained.Even or Odd CheckerPaste a whole list of numbers and get each one classified even or odd, with the counts and the parity rule explained — including 0 and negative numbers.

Open Greatest Common Factor Calculator and you get an answer straight away, with no account to create. It covers the Euclidean algorithm, prime factorisation and factor listing — adjust any of them and the result follows immediately.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Greatest Common Factor Calculator?

Find the GCF of up to 15 numbers with three methods side by side: the Euclidean algorithm, prime factorisation and factor listing.

What does it take into account?

It factors in the Euclidean algorithm, prime factorisation and factor listing. Change any of them and the output follows immediately.

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.

How is Greatest Common Factor Calculator different from Common Factor Calculator?

They sit next to each other but answer different questions: Common Factor Calculator is the one to open when you need it to find every common factor of 2 to 10 numbers, with the greatest common factor highlighted and coprime pairs flagged. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Factor Calculator is the closest one after this: List every divisor of a whole number in pairs, with the divisor count, the divisor sum, and whether it is prime, perfect, abundant or deficient.

What else is worth having open alongside it?

Prime Factor Calculator and Amicable Number Checker — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

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-toHow to Add and Subtract Fractions: Common Denominator, Combine, SimplifyYou can only add or subtract fractions that share a denominator. Learn to find a common denominator, combine the numerators, and simplify the result, with a worked example.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 Round Numbers: Round Half Up, Round Half to Even, and MoreRound to any decimal place or number of significant figures, and learn when to use round half up versus round half to even to avoid bias.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 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 Do Long Division: Divide, Multiply, Subtract, Bring DownLong division breaks a big division into a repeating four-step cycle. Learn the divide-multiply-subtract-bring-down loop and how to read the remainder, with a worked example.