GCF and LCM of 15 and 18
The greatest common factor and least common multiple of 15 and 18.
GCF of 15 and 18
3
LCM of 15 and 18
90
How it works
Break each number into its prime factors:
- 15 = 3 × 5
- 18 = 2 × 3²
The GCF (3) multiplies the primes both share, at the lowest power each appears. The LCM (90) multiplies every prime that appears in either number, at the highest power — which is also 15 × 18 ÷ 3 = 90.
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Frequently asked questions
What is the GCF of 15 and 18?+
The greatest common factor (GCF) of 15 and 18 is 3 — the largest number that divides both 15 and 18 with no remainder.
What is the LCM of 15 and 18?+
The least common multiple (LCM) of 15 and 18 is 90 — the smallest number that both 15 and 18 divide into. It equals 15 × 18 ÷ GCF = 270 ÷ 3 = 90.