GCF Calculator – Find the Greatest Common Factor Online
Find the greatest common factor (GCD) and least common multiple of two numbers.
About the GCF Calculator
What is the GCF Calculator?
A GCF calculator finds the greatest common factor (also called greatest common divisor, GCD) and least common multiple of two positive integers.
Why use this calculator?
GCF simplifies fractions and ratios; LCM finds common denominators. Both come up constantly in school maths and practical ratio problems.
How to use it
- Enter two positive integers.
- Read the GCF and LCM instantly.
- See the full factor list of each number for verification.
Formula
Euclid\u2019s algorithm; LCM = a × b ÷ GCF.
For lists of numbers use the separate LCM and common-factor calculators.
Frequently Asked Questions
Difference between GCF and HCF?
None — they are two names for the same value: the highest common factor.
What is the GCF of two primes?
If two numbers are prime and different, their GCF is 1 (they are coprime).
What order of operations does this use?
It follows standard PEMDAS/BODMAS rules: parentheses, exponents, multiplication and division, then addition and subtraction.
How precise are the answers?
The calculator uses double-precision floating-point math (about 15 significant digits) and rounds the display. For exact symbolic results use dedicated algebra software.
Can I enter negative numbers or decimals?
Yes. Negative values, decimals and very large or small numbers are all supported unless a field says otherwise.
What does it mean if I get an error?
Errors usually mean an invalid input, such as division by zero or a negative value where only positives make sense. Check your entries and try again.
Is this calculator free to use?
Yes. Every calculator on this site is completely free, with no hidden fees, no subscriptions and no limits on how many times you can use it.
How accurate are the results?
We use standard, widely accepted formulas and calculate in your browser using double-precision arithmetic. Results are rounded for readability, so treat them as reliable estimates rather than a guarantee. Real-world factors can vary the true figure.
Can I add this calculator to my own website?
Yes. Open this calculator page and use the "Add to your website" box in the sidebar to copy a ready-made iframe snippet, then paste it into any HTML page.
Does it work on a phone or tablet?
Yes. The layout is fully responsive, so it works on desktops, laptops, tablets and mobile phones, and every input adapts to touch screens.