Right Triangle Side Calculator

About this calculator

The Pythagorean theorem, a² + b² = c², relates the two legs of a right triangle to its hypotenuse, and rearranging it lets you solve for whichever side is missing given the other two — if you know one leg and the hypotenuse, the missing leg is √(c² − a²). Once all three sides are known, the triangle’s area follows immediately as half the product of the two legs.

This is one of the most-used formulas in practical trades: carpenters and framers use it to confirm a corner is square (the classic 3-4-5 rule is just a Pythagorean triple), roofers use it to find rafter lengths from rise and run, and surveyors and navigators use it to compute straight-line distances from two perpendicular offsets. It’s equally foundational in physics for resolving vector components and in construction and CAD software for validating right-angle geometry before cutting material.