GCF and LCM of 11 and 18

The GCF of 11 and 18 is 1. The LCM of 11 and 18 is 198.

• GCF (greatest common factor, also called GCD or HCF) of 11 and 18 = 1
• LCM (least common multiple) of 11 and 18 = 198

11 and 18 share no common factor except 1, so they are coprime (relatively prime). When two numbers are coprime their LCM is simply their product: 11 × 18 = 198.

Method 1: list the factors (GCF)

Factors of 11: 1, 11.
Factors of 18: 1, 2, 3, 6, 9, 18.
Common factors: 1. The greatest of these is 1.

Method 2: prime factorization

11 = 11 (prime)
18 = 2 × 3 × 3

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 × 11 = 198.

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. 18 = 1 × 11 + 7
2. 11 = 1 × 7 + 4
3. 7 = 1 × 4 + 3
4. 4 = 1 × 3 + 1
5. 3 = 3 × 1 + 0

The last non-zero remainder is 1, so GCF(11, 18) = 1.

LCM by listing multiples

Multiples of 11: 11, 22, 33, 44, 55, 66, 77, 88, 99, ...
Multiples of 18: 18, 36, 54, 72, 90, 108, 126, 144, 162, ...
The first number in both lists is 198.

Check: GCF × LCM = product

1 × 198 = 198 = 11 × 18. This always holds for two numbers, so you can find the LCM as (11 × 18) ÷ 1 = 198.

Simplifying the fraction 11/18

11/18 is already in lowest terms because the GCF of 11 and 18 is 1.

GCF and LCM of similar pairs

See also: factors of 11 · factors of 18 · 11/18 as a decimal.

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