GCF and LCM of 5 and 8

The GCF of 5 and 8 is 1. The LCM of 5 and 8 is 40.

• GCF (greatest common factor, also called GCD or HCF) of 5 and 8 = 1
• LCM (least common multiple) of 5 and 8 = 40

5 and 8 share no common factor except 1, so they are coprime (relatively prime). When two numbers are coprime their LCM is simply their product: 5 × 8 = 40.

Method 1: list the factors (GCF)

Factors of 5: 1, 5.
Factors of 8: 1, 2, 4, 8.
Common factors: 1. The greatest of these is 1.

Method 2: prime factorization

5 = 5 (prime)
8 = 2 × 2 × 2

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 × 2 × 2 × 5 = 40.

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. 8 = 1 × 5 + 3
2. 5 = 1 × 3 + 2
3. 3 = 1 × 2 + 1
4. 2 = 2 × 1 + 0

The last non-zero remainder is 1, so GCF(5, 8) = 1.

LCM by listing multiples

Multiples of 5: 5, 10, 15, 20, 25, 30, 35, 40, 45, ...
Multiples of 8: 8, 16, 24, 32, 40, 48, ...
The first number in both lists is 40.

Check: GCF × LCM = product

1 × 40 = 40 = 5 × 8. This always holds for two numbers, so you can find the LCM as (5 × 8) ÷ 1 = 40.

Simplifying the fraction 5/8

5/8 is already in lowest terms because the GCF of 5 and 8 is 1.

GCF and LCM of similar pairs

See also: factors of 5 · factors of 8 · 5/8 as a decimal.

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