Math
Pythagorean Theorem Calculator
Use this Pythagorean theorem calculator for right triangles when two sides are known and the third side is missing.
Missing side
—
- Triangle area
- —
- Perimeter
- —
Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the pythagorean theorem calculator solves
Use this Pythagorean theorem calculator for right triangles when two sides are known and the third side is missing.
Formula
How to use it
- Choose whether the missing side is the hypotenuse or a leg.
- Enter the two known side lengths.
- Use the side, area, and perimeter results together.
How to read the answer
The hypotenuse is always the longest side and sits across from the right angle.
Common mistakes and edge cases
- Only use this theorem for right triangles.
- The hypotenuse must be longer than either leg.
- Do not add side lengths before squaring them.
Worked examples
Classic 3-4-5 triangle
Missing side
5
Find a missing leg
Missing side
12
Frequently asked questions
Can this solve non-right triangles?+
No. Use a triangle calculator with the law of cosines for non-right triangles.
Which side is c?+
c is the hypotenuse, the side opposite the right angle.
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Last updated: May 8, 2026