# What is the Least Common Multiple of 18 and 42?

Least common multiple or lowest common denominator (lcd) can be calculated in two way; with the LCM formula calculation of greatest common factor (GCF), or multiplying the prime factors with the highest exponent factor.

Least common multiple (LCM) of 18 and 42 is 126.

LCM(18,42) = 126

LCM Calculator and
and

## Least Common Multiple of 18 and 42 with GCF Formula

The formula of LCM is LCM(a,b) = ( a × b) / GCF(a,b).
We need to calculate greatest common factor 18 and 42, than apply into the LCM equation.

GCF(18,42) = 6
LCM(18,42) = ( 18 × 42) / 6
LCM(18,42) = 756 / 6
LCM(18,42) = 126

## Least Common Multiple (LCM) of 18 and 42 with Primes

Least common multiple can be found by multiplying the highest exponent prime factors of 18 and 42. First we will calculate the prime factors of 18 and 42.

### Prime Factorization of 18

Prime factors of 18 are 2, 3. Prime factorization of 18 in exponential form is:

18 = 21 × 32

### Prime Factorization of 42

Prime factors of 42 are 2, 3, 7. Prime factorization of 42 in exponential form is:

42 = 21 × 31 × 71

Now multiplying the highest exponent prime factors to calculate the LCM of 18 and 42.

LCM(18,42) = 21 × 32 × 71
LCM(18,42) = 126