√18 =
3√2
≈ 4.242641
Square root of 18 — 4.242641 (3√2)
Irrational
The square root of 18 is about 4.242641, or exactly 3√2. It lies between 4 and 5.
- As a decimal
- ≈ 4.242641
- Simplified surd
- √18 = 3√2
- Between
- 4 < √18 < 5
- Squared
- 18² = 324
- Cube root
- ∛18 ≈ 2.620741
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.
√18 = √(9 × 2) = 3√2
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 18?
About 4.242641, or exactly 3√2.
Q. Can the surd be simplified?
Yes: 18 = 9 × 2, so 3 comes out and it becomes 3√2.
Q. Between which integers does it fall?
Between 4 and 5.
Q. What is the cube root of 18?
About 2.620741.