Square root of 16
√16 = 4. Here is why, drawn as a square and checked with a multiplication.
The answer
The square root of 16 is 4, because 4 × 4 = 16.
A note about this topic
England’s Year 5 curriculum includes recognising square numbers. The square-root explanations on this page are extension material.
16 drawn as a square
16 counters make a perfect square: 4 rows of 4. The length of the side is the square root.
How to work out √16
A square root asks: which number, times itself, makes 16? 4 × 4 = 16, so √16 = 4. Squaring and square rooting undo each other: 4 squared is 16, and the square root of 16 is 4.
There is a pattern in the square numbers too. Add up the first 4 odd numbers and you get 16: 1 + 3 + 5 + 7 = 16. Each new odd number is the extra row and column of counters that makes the next square.
4 × 4 is in the 4 times table, so that table gives you a way to recognise 16 as a square number.
Square numbers and their roots
The square numbers up to 144 are 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144.
More numbers
See every factor of 16 or check whether 16 is prime.
Questions parents ask
A square has an area of 16 cm². How long is each side?
4 cm, because 4 cm × 4 cm = 16 cm². Working out the side of a square from its area is finding a square root.
What is 16 squared?
16 × 16 = 256. Squaring 16 makes a much bigger number, while its square root, 4, is smaller.
Which square numbers come either side of 16?
9 (3 × 3) before it and 25 (5 × 5) after it. They are 7 below and 9 above 16.
Can a square root be negative?
Yes. −4 × −4 also makes 16, so −4 is a square root of 16 too. For a positive number, the symbol √ denotes the positive root, 4. The negative root also gives 16 when multiplied by itself.
Continue your number practice
Explore the diagnostic for another set of practice questions.