√81 =
9
Exact
Square root of 81 — 9
Exact
The square root of 81 is 9, because 9 × 9 = 81.
- As a decimal
- 9
- Simplified surd
- √81 = 9
- Between
- 9
- Squared
- 81² = 6561
- Cube root
- ∛81 ≈ 4.326749
How the surd is simplified
Pull out the largest square factor. Since 50 = 25 × 2, the root of 25 comes out as 5 and the 2 stays behind: 5√2.
√81 = √(81 × 1) = 9
Nearby numbers
From 1 to 200
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How to read this
- The decimal is rounded; the surd form is the exact value.
- Pulling out a square factor simplifies the surd — √50 = 5√2.
- If the number is not a perfect square, the decimal never ends (irrational).
- Knowing which two integers it sits between is enough to estimate in your head.
Frequently asked questions
Q. What is the square root of 81?
9 exactly.
Q. Can the surd be simplified?
Yes: 81 = 81 × 1, so 9 comes out and it becomes 9.
Q. Between which integers does it fall?
It is the whole number 9.
Q. What is the cube root of 81?
About 4.326749.