GCF for 15, 18 and 30

"Greatest Common Factor of 3 Numbers" Calculator
Greatest Common Factor of
,
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What's the Greatest Common Factor (GCF) of 15, 18 and 30?

Answer

GCF of 15, 18 and 30 is
3

Common factors: 1, 3

3 divides all three: 15 ÷ 3 = 5, 18 ÷ 3 = 6, 30 ÷ 3 = 10 — and 5, 6 and 10 have no factor but 1 common to all of them, so no larger number divides all three.

15 = 3 × 5

18 = 2 × 32

30 = 2 × 3 × 5

Prime151830Lowest power
2—22—
333233
55—5—

— = power 0: the prime is not a factor of this number, so it cannot be in the GCF.

GCF = 3

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GCF Table

1st2nd3rdGCF
1515183
1516181
1517181
1518183
1518191
1518201
1518213
1518221
1518231
1518243
1518251
1518261
1518273
1518281
1518291
1518303
1518311
1518321
1518333
1518341
1518351
1518363
1518371
1518381
1518393
1518401
1518411
1518423
1518431
1518441

FAQ

What's the Greatest Common Factor (GCF) of 15, 18 and 30?

GCF of 15, 18 and 30 is 3

What prime factors do 15, 18 and 30 share?

All three factorizations contain 3, and multiplying those shared primes gives 3 — exactly the greatest common factor.

Can you get the GCF of 15, 18 and 30 two numbers at a time?

Yes. The GCF of 15 and 18 is 3, and the GCF of 3 and 30 is 3 — the same answer, because the greatest common factor is associative and does not depend on the order of the three numbers.

How does the GCF simplify the ratio 15 : 18 : 30?

Divide every term by the GCF 3: 15 ÷ 3 = 5, 18 ÷ 3 = 6 and 30 ÷ 3 = 10. So 15 : 18 : 30 in lowest terms is 5 : 6 : 10, and no whole number other than 1 divides all three of those.

See Also