Need to find the missing side of a right triangle? This Pythagorean Theorem Calculator makes it fast and simple. Just enter the two known side lengths, and it calculates the hypotenuse instantly.

It’s useful for students, teachers, engineers, builders, DIYers, and anyone working with right triangles. Whether you’re checking homework, measuring a ramp, or planning a layout, this calculator saves time and reduces mistakes.

The Pythagorean theorem is one of the most important rules in geometry. It helps you connect the two shorter sides of a right triangle to the longest side, called the hypotenuse.

Instead of doing the square-and-square-root steps by hand, you can get the result in seconds and focus on the task at hand.

How to use this calculator

  1. Enter the length of Side A.

Type the first known side of the right triangle into the Side A field. You can use any non-negative value within the allowed range.

  1. Enter the length of Side B.

Add the second known side length in the Side B field. The calculator uses both values to determine the missing side.

  1. Read the hypotenuse result.

The calculator applies the Pythagorean theorem and shows the hypotenuse, along with the squared values of both sides. This makes it easy to check the calculation step by step.

Formula

The Formula

The Pythagorean theorem applies to right triangles only. It says that the square of the hypotenuse is equal to the sum of the squares of the other two sides:

c = √(a² + b²)

Here, the calculator first squares Side A and Side B, adds those results together, and then takes the square root to find the hypotenuse.

Variables

  • a = Side A, one of the two shorter sides of the right triangle
  • b = Side B, the other shorter side of the right triangle
  • c = Hypotenuse, the longest side opposite the right angle

The detail outputs show a² and b² so you can see exactly how the final answer is built.

Examples

Example 1: A 3-4-5 triangle

Suppose Side A = 3 units and Side B = 4 units. The calculator squares both values: 3² = 9 and 4² = 16. Then it adds them: 9 + 16 = 25.

Finally, it takes the square root of 25, which gives a hypotenuse of 5.00 units. This is the classic right-triangle example many people learn first.

Example 2: A larger triangle

Suppose Side A = 8 units and Side B = 15 units. The calculator finds 8² = 64 and 15² = 225. Adding them gives 289.

The square root of 289 is 17.00 units, so the hypotenuse is 17.00 units. This shows how the same formula works for both small and larger measurements.

Frequently asked questions

What does the Pythagorean theorem calculator find?
It finds the hypotenuse of a right triangle when you know the lengths of the other two sides. It also shows the squared values of each side so you can follow the calculation.
Do the two sides have to be in the same units?
Yes. Side A and Side B should use the same unit type, such as meters, feet, or inches. The result will be in that same unit.
Can I use this calculator for any triangle?
No. The Pythagorean theorem only works for right triangles, meaning triangles with one 90-degree angle. It does not apply to triangles without a right angle.
How accurate is the result?
The calculator uses the standard Pythagorean formula and rounds the final answer to two decimal places. For most everyday uses, that level of precision is enough.
What if one of the sides is zero?
A side length of zero does not form a valid triangle, so the result would not represent a real right triangle. Both sides should be positive values for a meaningful calculation.