Pythagorean Theorem Calculator
Find the missing side of a right triangle using a² + b² = c².
Enter any two sides — the missing side is calculated automatically. Leave one field blank.
Common Pythagorean Triples
Frequently Asked Questions
What is the Pythagorean theorem?▼
In a right triangle, the square of the hypotenuse (longest side) equals the sum of squares of the other two sides: a² + b² = c². Named after Pythagoras (~570–495 BC), though known to Babylonian mathematicians 1,000 years earlier.
What is a Pythagorean triple?▼
A Pythagorean triple is a set of three positive integers (a, b, c) that satisfy a² + b² = c². The simplest is (3, 4, 5): 9 + 16 = 25. Multiples of any triple are also triples: (6, 8, 10), (9, 12, 15).
How do you find the hypotenuse?▼
Given legs a and b: c = √(a² + b²). For example, a=3, b=4: c = √(9+16) = √25 = 5.
How do you find a leg given the hypotenuse?▼
Given hypotenuse c and one leg a: b = √(c² − a²). For example, c=13, a=5: b = √(169−25) = √144 = 12.