Cube Root Calculator
Calculate the cube root of any number, including negatives and decimals, or switch to a square root, 4th root or any nth root. The calculator tells you whether the number is a perfect cube and simplifies radicals such as ∛54 = 3∛2.
Whole number, decimal or negative (odd roots)
How to use the Cube Root Calculator
- Enter a number: whole, decimal or negative.
- Choose the root: cube root by default, or square, 4th, 5th, 6th or a custom nth root.
- Press Calculate root (results also update as you type).
- Read the root, whether it is a perfect cube and the simplified radical form.
Cube root formula
- Definition: ∛x = r means r³ = x; equivalently ∛x = x1/3.
- nth root: ⁿ√x = x1/n, the number r with rn = x.
- Product rule: ∛(a × b) = ∛a × ∛b, which is how radicals are simplified: ∛54 = ∛27 × ∛2 = 3∛2.
- Negative numbers: ∛(−x) = −∛x for odd roots.
- Newton's method: rnext = r − (r³ − x) ÷ (3r²) converges quickly to ∛x.
Table of perfect cubes
| n | n³ | n | n³ | n | n³ |
|---|---|---|---|---|---|
| 1 | 1 | 8 | 512 | 15 | 3,375 |
| 2 | 8 | 9 | 729 | 16 | 4,096 |
| 3 | 27 | 10 | 1,000 | 17 | 4,913 |
| 4 | 64 | 11 | 1,331 | 18 | 5,832 |
| 5 | 125 | 12 | 1,728 | 19 | 6,859 |
| 6 | 216 | 13 | 2,197 | 20 | 8,000 |
| 7 | 343 | 14 | 2,744 | 25 | 15,625 |
Cube roots of common non-perfect cubes
| x | ∛x (approx.) | Simplified |
|---|---|---|
| 2 | 1.259921 | ∛2 |
| 3 | 1.442250 | ∛3 |
| 10 | 2.154435 | ∛10 |
| 16 | 2.519842 | 2∛2 |
| 24 | 2.884499 | 2∛3 |
| 54 | 3.779763 | 3∛2 |
| 81 | 4.326749 | 3∛3 |
| 100 | 4.641589 | ∛100 |
| 250 | 6.299605 | 5∛2 |
Frequently asked questions
What is a cube root?
The cube root of x is the number that, multiplied by itself three times, gives x. ∛27 = 3 because 3 × 3 × 3 = 27. It is the same as raising x to the power 1/3.
Can you take the cube root of a negative number?
Yes. Unlike square roots, odd roots of negative numbers are real: ∛−125 = −5 because (−5)³ = −125. Even roots (square, 4th…) of negative numbers are not real numbers.
How do you simplify a cube root?
Factor the number into primes and pull out every group of three equal factors. 54 = 2 × 3³, so ∛54 = 3∛2. 250 = 2 × 5³, so ∛250 = 5∛2.
How do I know if a number is a perfect cube?
Its cube root is a whole number, or equivalently every exponent in its prime factorization is a multiple of 3. 216 = 2³ × 3³ is a perfect cube (6³); 200 = 2³ × 5² is not.
What is the nth root?
The nth root of x is the number r with rⁿ = x, written ⁿ√x or x^(1/n). The square root is n = 2 and the cube root is n = 3. The 5th root of 3125 is 5 because 5⁵ = 3125.
How do you estimate a cube root by hand?
Find the perfect cubes on either side. 50 lies between 27 (3³) and 64 (4³), so ∛50 is between 3 and 4, closer to 4. A Newton step r − (r³ − x)/(3r²) from r = 4 gives about 3.69; the exact value is 3.684.