Pythagorean Theorem Calculator
Enter two sides of a right triangle to find the third with a² + b² = c².
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The theorem
In a right triangle, the square of the longest side (the hypotenuse, opposite the right angle) equals the sum of the squares of the other two sides: a² + b² = c². So c = √(a² + b²), and a missing leg is b = √(c² − a²).
Practical uses
- Checking a right angle on site: mark 3 m along one wall and 4 m along the other. The diagonal should be exactly 5 m (the 3-4-5 rule).
- Ladder length: a ladder reaching 4 m up a wall from 1.5 m away needs to be √(16 + 2.25) ≈ 4.27 m.
- Screen size: a 16:9 screen 52 cm wide and 29 cm high has a diagonal of about 59.5 cm (23.4 inches).
Whole-number solutions such as (3, 4, 5), (5, 12, 13) and (8, 15, 17) are called Pythagorean triples. The calculator tells you when you have one.
Free to useNo software to install — works in any modern browser.
No signup neededOpen the tool and start straight away.
Runs in your browserNothing you enter is sent to a server.
Works on mobileSame tool on your phone, tablet or desktop.
How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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