GCF and LCM of 20 and 36

The GCF of 20 and 36 is 4. The LCM of 20 and 36 is 180.

• GCF (greatest common factor, also called GCD or HCF) of 20 and 36 = 4
• LCM (least common multiple) of 20 and 36 = 180

Method 1: list the factors (GCF)

Factors of 20: 1, 2, 4, 5, 10, 20.
Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36.
Common factors: 1, 2 and 4. The greatest of these is 4.

Method 2: prime factorization

20 = 2 × 2 × 5
36 = 2 × 2 × 3 × 3

GCF: multiply the prime factors both numbers share: 2 × 2 = 4.

LCM: multiply every prime the maximum number of times it appears in either number: 2 × 2 × 3 × 3 × 5 = 180.

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. 36 = 1 × 20 + 16
2. 20 = 1 × 16 + 4
3. 16 = 4 × 4 + 0

The last non-zero remainder is 4, so GCF(20, 36) = 4.

LCM by listing multiples

Multiples of 20: 20, 40, 60, 80, 100, 120, 140, 160, 180, ...
Multiples of 36: 36, 72, 108, 144, 180, 216, ...
The first number in both lists is 180.

Check: GCF × LCM = product

4 × 180 = 720 = 20 × 36. This always holds for two numbers, so you can find the LCM as (20 × 36) ÷ 4 = 180.

Simplifying the fraction 20/36

Divide the top and bottom by the GCF 4: 20/36 = 5/9.

GCF and LCM of similar pairs

See also: factors of 20 · factors of 36.

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