GCF Calculator
Enter two or more whole numbers to find the biggest number that divides into all of them. We show the LCM alongside.
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The formula
Euclid: GCF(a, b) = GCF(b, a mod b), repeated until the remainder is 0.
What the GCF is
The greatest common factor, also called the greatest common divisor (GCD) or highest common factor, is the largest number that divides into every number you gave. For 24 and 36 it is 12.
Why it is useful
You use it to simplify fractions (divide top and bottom by the GCF), to split things into equal groups without leftovers, and to tile a rectangle with the largest possible square tiles. A 24 by 36 floor can be covered with 12 by 12 tiles with nothing cut.
The Euclidean method
This 2,300-year-old trick is how the calculator works. To find the GCF of 48 and 18: 48 divided by 18 leaves 12. Then 18 divided by 12 leaves 6. Then 12 divided by 6 leaves 0. The last non-zero remainder, 6, is the answer.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Whole numbers (separated by commas or spaces): 12 18 | Greatest common factor (GCF): 6 |
| Whole numbers (separated by commas or spaces): 4 6 10 | Greatest common factor (GCF): 2 |
| Whole numbers (separated by commas or spaces): 24 36 60 | Greatest common factor (GCF): 12 |
| Whole numbers (separated by commas or spaces): 7 11 | Greatest common factor (GCF): 1 |
GCF Calculator: frequently asked questions
What if the GCF is 1?
The numbers are called coprime or relatively prime. They share no factor except 1, so a fraction made from them cannot be simplified.
Is GCF the same as GCD?
Yes. GCF, GCD and HCF are three names for the same thing.
How accurate is this calculator?
It uses standard double-precision arithmetic, accurate to about 15 significant digits. Results are rounded only for display.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026