√81 = 9. The square root of 81 is 9, because 9 × 9 = 81. 81 is a perfect square.
√81 at a glance.
Value
9
Rounded
9
Perfect square?
Yes
81 squared
6,561
Checking it in your head
A perfect square's root is a whole number, so check by multiplying back: 9 × 9 = 81. Its last digit fits too: squares only ever end in 0, 1, 4, 5, 6 or 9, and 9² ends in 1.
Frequently asked questions
What is the square root of 81?
The square root of 81 is 9, because 9 × 9 = 81. 81 is a perfect square.