Square roots·√21
√21 =
√21
≈ 4.582576

Square root of 21 — 4.582576 (√21)

Irrational

The square root of 21 is about 4.582576, or exactly √21. It lies between 4 and 5.

As a decimal
≈ 4.582576
Simplified surd
√21 = √21
Between
4 < √21 < 5
Squared
21² = 441
Cube root
∛21 ≈ 2.758924

Nearby numbers

√18 = 3√2√19 = √19√20 = 2√5√22 = √22√23 = √23√24 = 2√6

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 21?

About 4.582576, or exactly √21.

Q. Can the surd be simplified?

No — there is no square factor to pull out.

Q. Between which integers does it fall?

Between 4 and 5.

Q. What is the cube root of 21?

About 2.758924.