The quickest way to find a cube root
Most calculators have a cube root button or a way to reach one through a menu. On a scientific calculator, look for a button labeled ∛x or ∛ — it often shares a key with the square root button. Press the button, type your number, and press equals. On a graphing calculator like a TI-84, go to the Math menu, select Cube Root (usually option 4), type your number in the parentheses, and press Enter.
If your calculator has no cube root button at all, you can use the exponent method instead: type your number, press the exponent button (usually ^ or x^y), type 1/3, and press equals. This works because a cube root is the same as raising a number to the power of one-third.
Key Takeaways
- Scientific calculators usually have a dedicated cube root button (∛x) that you access directly or through a shift key.
- Graphing calculators like the TI-84 hide the cube root in the Math menu under option 4 or similar.
- Any calculator with an exponent button can find cube roots by raising the number to the power of 1/3.
- The exponent method works on phone calculators and spreadsheets when a cube root button is not available.
Finding the cube root button on a scientific calculator
On most scientific calculators, the cube root button sits on the same key as the square root button. You reach it by pressing Shift or 2nd first, then the square root button. The button itself is usually labeled with a small 3 above or before the radical sign (∛). After you press Shift and the cube root button, type the number you want the cube root of and press equals.
Some older or simpler scientific calculators do not have a cube root button at all. If you cannot find ∛ anywhere on your calculator, even after checking the Shift menu, move to the exponent method described below.
Using the cube root function on a graphing calculator
On a TI-84 or similar graphing calculator, the cube root lives in the Math menu. Press the Math button, then use the arrow keys to scroll down until you see Cube Root or ∛(. It is usually near the top of the list, often as option 4. Press the number next to it or highlight it and press Enter.
The calculator will show ∛( on your screen with the cursor ready for input. Type the number you want the cube root of, close the parenthesis by pressing ), and press Enter. The answer appears on the next line.
The exponent method: raising to the power of 1/3
Any calculator that has an exponent button can find a cube root without a dedicated button. The trick is that a cube root is mathematically the same as raising a number to the power of 1/3. So to find the cube root of 27, you type: 27 ^ (1/3) and press equals. The answer is 3.
On most calculators, the exponent button is labeled ^ or x^y. After you type your number and press the exponent button, you must type the fraction 1/3 in parentheses: (1/3). The parentheses tell the calculator to treat 1/3 as a single exponent, not to divide 1 by 3 first and then use that decimal. Without parentheses, some calculators will give you the wrong answer.
Using cube root on a phone calculator or computer
The calculator app on most phones does not show a cube root button in standard view. Switch to Scientific mode (usually a menu option or a sideways rotation on your phone) and you will see more buttons, including the cube root. Look for ∛ or a button labeled with a 3 and a radical sign. Tap it, type your number, and tap equals.
If your phone calculator still has no cube root button even in Scientific mode, use the exponent method: type your number, tap the button labeled ^ or x^y, type (1/3), and tap equals. On a computer spreadsheet like Excel or Google Sheets, type =27^(1/3) in a cell to find the cube root of 27. The answer will appear when you press Enter.
What to do if your answer looks wrong
Cube roots of negative numbers sometimes cause confusion. A negative number does have a cube root — for example, the cube root of −8 is −2, because −2 × −2 × −2 = −8. However, some calculators will show an error or a complex number instead. This is a limitation of the calculator, not a sign that you did something wrong. If you need the cube root of a negative number and your calculator refuses, take the cube root of the positive version of that number and add a negative sign to the answer.
If your answer is a long decimal like 2.9999999 when you expect 3, you have found the right answer — the extra digits are just rounding error from how the calculator does math internally. Round to the number of decimal places you need.
Frequently Asked Questions
What is the difference between the cube root button and the exponent method?
They give the same answer. The cube root button is faster if your calculator has one. The exponent method works on any calculator with a ^ button, so it is more universal. Use whichever your calculator makes easiest.
Do I need parentheses around the 1/3 when I use the exponent method?
Yes, on most calculators. Without parentheses, the calculator may divide 1 by 3 first and then raise your number to that decimal, which can give a slightly different answer due to rounding. Parentheses tell the calculator to treat 1/3 as a single unit.
Why does my calculator show an error when I try to find the cube root of a negative number?
Some calculators are programmed to reject negative inputs for the cube root function, even though negative numbers do have cube roots. If this happens, find the cube root of the positive version of the number and then add a negative sign to your answer.
Can I find a cube root on a basic four-function calculator?
No. A basic calculator with only +, −, ×, and ÷ buttons cannot find cube roots. You need either a scientific calculator with a cube root button or any calculator with an exponent button so you can use the 1/3 power method.