How do you do the Pythagorean theorem on a calculator?
Square the first side, add the square of the second, then press the square root key. For legs 3 and 4 that is 3 x² + 4 x² =, which gives 25, then √ gives 5.
By Mateo Díaz · Last updated: July 19, 2026
Pythagorean theorem calculator
Tap a side to solve for it - the dashed side is the one being calculated.
- Hypotenuse c
- 5
- Perimeter
- 12
- Area
- 6
- Angle opposite leg a
- 36.87°
- Angle opposite leg b
- 53.13°
c = √(3² + 4²) = √25 = 5
The full answer
On a scientific calculator
Finding the hypotenuse for legs 3 and 4:
| Step | Keys | Display |
|---|---|---|
| Square the first leg | 3 x² | 9 |
| Add the square of the second | + 4 x² = | 25 |
| Take the square root | √ (then = on some models) | 5 |
On calculators where √ acts on the next entry instead of the last answer, use the answer-recall key: √ ANS =.
Solving for a leg instead
Subtract instead of adding, hypotenuse first. For hypotenuse 13 and leg 5: 13 x² - 5 x² = gives 144, then the square root gives 12.
On a basic or phone calculator
No x² key? Multiply each side by itself: 3 × 3 + 4 × 4 = gives 25. Most phone calculators reveal x² and √ when you rotate the phone to landscape.
Skip the keystrokes
The calculator on this page does the whole thing in one go - enter the two sides and it returns the third along with the exact substitution line, so you can still copy the working. For general keystroke math, our scientific calculator has x², √, and answer recall.