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Pythagorean Theorem Calculator

Choose which side you want to find, type the two numbers you already know, and press Calculate to get the missing side of a right triangle. The answer shows in a card below the button, where you can copy it or clear the form.

What this calculator does

The form has a Solve for select with three options, Hypotenuse (c), Leg (a) and Leg (b), three number fields named Leg (a), Leg (b) and Hypotenuse (c), and a Calculate button.

The calculation runs only when the Calculate button is pressed, and the result appears in cards below the button. Copy writes a result and its unit to the clipboard, and Clear resets the form so you can start another triangle.

For example, with Solve for set to Hypotenuse (c), Leg (a) entered as 3 and Leg (b) entered as 4, the tool returns Hypotenuse (c): 5.

Pythagorean theorem formula

In a right triangle the two shorter sides are the legs, a and b, which meet at the right angle, and the hypotenuse, c, is the side opposite the right angle. The theorem says that the square of the hypotenuse equals the sum of the squares of the two legs, so the hypotenuse is found as c = √(a² + b²).

Solving the same relationship for a leg gives a = √(c² − b²) and b = √(c² − a²). That is why finding a leg takes the hypotenuse and the other leg as its two inputs.

Working with the results

With the legs 1.5 and 2, the tool reports Hypotenuse (c): 2.5, following c = √(1.5² + 2²) = √(6.25) = 2.5. Two equal legs of 1 give c = √(1² + 1²) = √2, shown as ≈ 1.4142135623731 because that length is not a whole number.

The same works in reverse: with Leg (b) 12 and Hypotenuse (c) 13 the tool gives Leg (a): 5 from a = √(13² − 12²) = √(25) = 5, and with Leg (a) 8 and Hypotenuse (c) 17 it gives Leg (b): 15 from b = √(17² − 8²) = √(225) = 15.