GCF Calculator finds the greatest common factor — the largest whole number that divides every number in a list evenly — for two, three, or more integers at once. Type your numbers separated by commas, spaces, or new lines and it reduces them pairwise with the Euclidean algorithm, then shows the matching least common multiple and a prime factor breakdown for each number so you can see exactly how the result was reached. It is handy for reducing fractions to lowest terms, splitting items into equal groups, scheduling repeating events, and checking homework by hand. Built for students, teachers, and anyone who needs a fast, accurate GCF (also called the GCD or highest common factor) without long division on paper. Everything runs locally in your browser.
Features
Finds the GCF (GCD) of two or more positive whole numbers at once
Accepts numbers separated by commas, spaces, or new lines
Shows the matching least common multiple (LCM) alongside the GCF
Displays a prime factor breakdown for every number you enter
Uses the Euclidean algorithm, reduced pairwise across the whole list
Clear error message when input has fewer than two numbers or isn't a whole number
Copy a plain-text summary of the numbers, GCF, and LCM in one click
Runs entirely in your browser with no numbers sent anywhere
How to use the GCF Calculator
Type two or more positive whole numbers into the Numbers field
Separate each number with a comma, space, or new line
Read the GCF and LCM in the Result panel
Check the prime factor breakdown to see how the GCF was derived
Copy the summary with the copy button
Example
Input
12, 18
Output
GCF: 6
12 = 2^2 x 3 and 18 = 2 x 3^2 share 2 x 3 = 6, so the GCF Calculator returns 6 (and an LCM of 36).
Common errors & troubleshooting
The GCF Calculator shows an error instead of a result. — Enter at least two positive whole numbers — decimals, negative signs, and text like 'twelve' are not accepted, only digits.
The result seems too small for large, similar-looking numbers. — The GCF only counts shared prime factors — two large numbers can still share just a single small factor, like 100 and 63 sharing only 1.
Not sure whether to use GCF or LCM for a word problem. — Use the GCF when splitting things into the largest equal groups (fraction reduction, dividing items evenly); use the LCM when finding when repeating events line up again.
One of the numbers is 1. — The GCF of any list that includes 1 is always 1, since 1 has no other factors — the tool still shows the LCM of the remaining numbers correctly.
Frequently asked questions
What is the GCF Calculator?
It is a tool that finds the greatest common factor (also called the GCD or highest common factor) of two or more positive whole numbers, using the Euclidean algorithm, and also shows the least common multiple and a prime factor breakdown.
How does the GCF Calculator find the greatest common factor?
It reduces the list pairwise with the Euclidean algorithm: it finds the GCD of the first two numbers, then finds the GCD of that result with the next number, and so on until one value — the GCF — remains.
Can the GCF Calculator handle more than two numbers?
Yes. Enter any number of positive whole numbers separated by commas, spaces, or new lines, and the GCF Calculator finds the greatest common factor shared by the entire list.
Does the GCF Calculator also give the LCM?
Yes. Alongside the greatest common factor, the result panel shows the least common multiple of the same list of numbers.
What numbers can I type into the GCF Calculator?
Enter two or more positive whole numbers. Decimals, negative numbers, and non-numeric text are not supported — the tool shows an error message so you can correct the input.
Is my number list uploaded when I use the GCF Calculator?
No. The GCF Calculator runs entirely in your browser — the numbers you type are computed on your device and are never sent to ArrayKit or anywhere else.
Related tools
LCM Calculator — Find the least common multiple of two or more integers with the steps.
Factor Calculator — List all factors of a number and its prime factorization.
Fraction Calculator — Add, subtract, multiply and divide fractions and simplify the result.
Ratio Calculator — Simplify ratios and solve proportions for a missing value.