Right triangle calculator
Pythagoras from two sides, and everything else that follows: area, perimeter, both acute angles, and the height to the hypotenuse. This is also the calculation behind squaring a corner on site.
Hypotenuse5.0000
- Side a
- 3.0000
- Side b
- 4.0000
- Area
- 6.0000
- Perimeter
- 12.0000
- Angle opposite a
- 36.87
- Angle opposite b
- 53.13
- Height to the hypotenuse
- 2.4000
- Inscribed circle radius
- 1.0000
The formula
a² + b² = c². Area = ab/2. The angles come from arctan(a/b) and its complement, since the two acute angles sum to 90°. The height to the hypotenuse is ab/c.
Worked example
Sides of 3 and 4 give a hypotenuse of exactly 5, an area of 6, a perimeter of 12, and angles of 36.87° and 53.13°.
How to use it
- 1The hypotenuse is always the longest side, opposite the right angle. The calculator rejects a hypotenuse shorter than a leg.
- 2Units do not matter as long as both inputs use the same one; the area comes out in those units squared.
- 3To square a corner on site, measure 3 along one edge and 4 along the other. If the diagonal is exactly 5, the corner is square.
Questions people ask
What are Pythagorean triples?
Whole-number right triangles: 3-4-5, 5-12-13, 8-15-17 and their multiples. Builders use them because they need no decimals and no calculator.
Does this work for other triangles?
No, it assumes a right angle. For any other triangle you need the law of cosines, c² = a² + b² − 2ab·cos(C).
Last reviewed: 2026-10-20