GCF and LCM of 18 and 23

The GCF of 18 and 23 is 1. The LCM of 18 and 23 is 414.

• GCF (greatest common factor, also called GCD or HCF) of 18 and 23 = 1
• LCM (least common multiple) of 18 and 23 = 414

18 and 23 share no common factor except 1, so they are coprime (relatively prime). When two numbers are coprime their LCM is simply their product: 18 × 23 = 414.

Method 1: list the factors (GCF)

Factors of 18: 1, 2, 3, 6, 9, 18.
Factors of 23: 1, 23.
Common factors: 1. The greatest of these is 1.

Method 2: prime factorization

18 = 2 × 3 × 3
23 = 23 (prime)

GCF: multiply the prime factors both numbers share: there are none, so the GCF is 1.

LCM: multiply every prime the maximum number of times it appears in either number: 2 × 3 × 3 × 23 = 414.

Method 3: Euclidean algorithm (GCF)

Divide the larger number by the smaller and repeat with the remainder until it is 0. The last non-zero remainder is the GCF.

1. 23 = 1 × 18 + 5
2. 18 = 3 × 5 + 3
3. 5 = 1 × 3 + 2
4. 3 = 1 × 2 + 1
5. 2 = 2 × 1 + 0

The last non-zero remainder is 1, so GCF(18, 23) = 1.

LCM by listing multiples

Multiples of 18: 18, 36, 54, 72, 90, 108, 126, 144, 162, ...
Multiples of 23: 23, 46, 69, 92, 115, 138, 161, 184, 207, ...
The first number in both lists is 414.

Check: GCF × LCM = product

1 × 414 = 414 = 18 × 23. This always holds for two numbers, so you can find the LCM as (18 × 23) ÷ 1 = 414.

Simplifying the fraction 18/23

18/23 is already in lowest terms because the GCF of 18 and 23 is 1.

GCF and LCM of similar pairs

See also: factors of 18 · factors of 23.

Different numbers? Use the GCF and LCM calculator (any amount of numbers) or browse all GCF and LCM pairs.