How to find the factors of 18
Test every whole number from 1 up to the square root of 18 (√18 ≈ 4.243). Each number that divides evenly gives you two factors at once: the divisor and the quotient.
- 18 ÷ 1 = 18 — so 1 and 18 are factors
- 18 ÷ 2 = 9 — so 2 and 9 are factors
- 18 ÷ 3 = 6 — so 3 and 6 are factors
- 18 ÷ 4 = 4.5 — not a whole number
Collecting both numbers from every successful division gives the complete list: 1, 2, 3, 6, 9 and 18.
Prime factorization of 18
Divide by the smallest prime that fits, and keep going until the quotient is 1:
The primes you divided by give 18 = 2 × 3². From the exponents you can also count the factors without listing them: (1 + 1) × (2 + 1) = 6.
Properties of 18
- 18 is a composite number.
- The sum of all its factors is 39; the sum of its proper factors (excluding 18) is 21, which makes it a abundant number (its proper factors add up to more than itself).
- 18 is not a perfect square, so its factors pair up evenly.
- Multiples of 18 include 36, 54, 72, 90 and so on.
Factors vs. multiples
Factors of 18 are the numbers that divide into it; multiples of 18 are the numbers it divides into. Every number has a limited set of factors but infinitely many multiples. To work with any other number, use the factors calculator, or find shared factors with the GCF calculator.
Frequently asked questions
What are the factors of 18?
The factors of 18 are 1, 2, 3, 6, 9 and 18. Each of these divides 18 with no remainder.
How many factors does 18 have?
18 has 6 positive factors, which form 3 factor pairs. Counting negative factors as well doubles that to 12.
What is the prime factorization of 18?
18 = 2 × 3². Its distinct prime factors are 2 and 3.
Is 18 a prime number?
No. 18 is composite because it has 6 factors, more than the two a prime number has.