Quick answer: The common factors of 12, 18 and 24 are 1, 2, 3 and 6: their greatest common factor is 6, and every common factor divides 6.
How it's calculated
A common factor divides every number in the list with no remainder. Listing all factors of each number and keeping the ones that appear in every list gives the answer.
A shortcut: the common factors are exactly the factors of the greatest common factor. Find the GCF (the GCF calculator shows Euclid's steps), then list its factors.
To see one number's factors and factor pairs, use the factor calculator.
Worked examples
- 12, 18 and 24: GCF 6 → 1, 2, 3, 6
- 36 and 60: GCF 12 → 1, 2, 3, 4, 6, 12
- 8 and 15: GCF 1 → 1
Frequently asked questions
Is 1 always a common factor?
Yes. 1 divides every whole number, so it is a common factor of any list. If it is the only one, the numbers are coprime.
What is the difference between common factors and common multiples?
Common factors divide into all the numbers (they are small); common multiples are divisible by all of them (they are large). See the LCM calculator.
How many numbers can I enter?
Up to 20 whole numbers, each up to one trillion.
What are the common factors of 12, 18 and 24?
1, 2, 3 and 6. The biggest one, 6, is their GCF.
What are common factors actually used for?
Simplifying fractions and ratios, and splitting things into equal groups. With 12, 18 and 24 items you can make at most 6 equal groups with nothing left over.
What if the only common factor is 1?
Then the numbers are coprime. Two different primes always are, but numbers don't have to be prime to be coprime: 8 and 15 are.