Factors of 18
Every whole number that divides 18 exactly, the factor pairs, and how to find them yourself.
The answer
The factors of 18 are 1, 2, 3, 6, 9 and 18.
Factor pairs of 18
| Pair | Makes |
|---|---|
| 1 × 18 | 18 |
| 2 × 9 | 18 |
| 3 × 6 | 18 |
Prime factors of 18
- Prime factorisation
- 18 = 2 × 3 × 3 (2 × 3²)
- Is 18 prime?
- No. It has 6 factors, not just 1 and 18.
- Is 18 a square number?
- No. 4 × 4 = 16 and 5 × 5 = 25, so 18 falls between two square numbers.
How to find the factors of 18
18 is even, so 2 is sure to be a factor. Its digits add up to 9, a multiple of 9, so 3 and 9 are factors. Work up from 1 to 4, and write down both numbers in every pair you find.
- 18 ÷ 1 = 18, so 1 × 18 is a pair.
- 18 ÷ 2 = 9, so 2 × 9 is a pair.
- 18 ÷ 3 = 6, so 3 × 6 is a pair.
- 4 does not go into 18 exactly.
Stop at 5: 5 × 5 = 25, which is more than 18. The next pair you would find is 6 × 3, which is 3 × 6 turned round, so you already have every pair.
18 in the times tables
2 × 9 = 18 and 3 × 6 = 18. Practise the 2 times table, 3 times table, 6 times table and 9 times table.
More numbers
Check whether 18 is prime.
Questions parents ask
What is the largest factor of 18, apart from 18 itself?
9. Divide 18 by its smallest factor above 1, which is 2: 18 ÷ 2 = 9.
What do the factors of 18 add up to?
39. Leaving out 18 itself, they add up to 21, which is more than 18, so 18 is called an abundant number.
Which number after 18 has the same number of factors?
20. Like 18, it has exactly 6 factors.
Number facts are the base of 11+ maths
Factors, multiples, primes and square numbers come up all over 11+ maths, from simplifying fractions to ratio. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.