**The square root of 40 is 6.3245553.** The square root of 40 is also written as 2√10. Numbers that are perfect squares have a whole number as their square roots.

Numbers such as 4, 9, 16 and 25 are perfect squares. Their square roots are 2, 3, 4 and 5, respectively. However, the prime factors of 40 are 2 x 2 x 2 x 5. This indicates that 40 is not a perfect square, as each prime factor must be present in multiples of 2 for a number to be a square. The prime factors of 36 are 2 x 2 x 3 x 3, and this shows that the square root of 36 is 2 x 3, which equals 6.