MATHS & STATISTICS / ALGEBRA

Root calculator: square, cube and nth roots

Find the square root, cube root or any nth root of a number, including odd roots of negative numbers.

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Your numbers

2 = square root, 3 = cube root.
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YOUR RESULT

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WORKED EXAMPLE

Root calculator: square, cube and nth roots: a worked example

With number (x) 729, root degree (n) 3, the root is 9.

Inputs
Number (x)729
Root degree (n)3
Results
Root9
Square root27
Cube root9
THE METHOD

How it works

Enter the number and the degree of the root: 2 for a square root, 3 for a cube root and so on. The nth root is the number that gives x when raised to the power n. Even roots of negative numbers are not real numbers, while odd roots of negative numbers are simply negative. The square root and cube root are shown alongside for comparison.

Formulaⁿ√x = x^(1/n). An odd root of a negative number is negative: ³√(−27) = −3.
ASSUMPTIONS

Assumptions and limits

  • Only real roots are shown: the principal (non-negative) root for even degrees and the single real root for odd degrees.
  • The degree is a whole number from 2 to 100.
  • Results are shown to ten significant figures, so irrational roots such as √2 are rounded.
  • Results are estimates based on the inputs and assumptions on this page, not professional advice.
  • Try this: use “Save scenario A”, change one input and compare the two results side by side.
QUESTIONS

Frequently asked questions

How is the result of the “Root calculator: square, cube and nth roots” calculated?

ⁿ√x = x^(1/n). An odd root of a negative number is negative: ³√(−27) = −3. Enter the number and the degree of the root: 2 for a square root, 3 for a cube root and so on. The nth root is the number that gives x when raised to the power n. Even roots of negative numbers are not real numbers, while odd roots of negative numbers are simply negative. The square root and cube root are shown alongside for comparison.

What does the worked example show?

With number (x) 729, root degree (n) 3, the root is 9. Square root: 27; Cube root: 9.

What assumptions and limits apply?

This is an estimate based on the inputs and assumptions shown on this page, not professional advice. Check anything with financial, health or safety consequences independently.

Is my data private?

Yes. Calculations run in your browser and your numbers are not sent to a server. A share link contains the inputs you choose to share, so check it before sending it to anyone.

What is the cube root of 729?

9, because 9 × 9 × 9 = 729.

Why does √9 give 3 and not −3?

Both 3 and −3 square to 9, but the √ symbol means the principal root, which is the non-negative one. Equations like x² = 9 have both answers: x = 3 or x = −3.

How do I estimate a square root by hand?

Find the perfect squares on either side. √50 lies between √49 = 7 and √64 = 8, close to 7. Refine with the average of 7 and 50 ÷ 7: (7 + 7.14) ÷ 2 ≈ 7.07, which is accurate to two decimals.

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