Right Triangle Calculator
From the two legs of a right triangle, get the hypotenuse, the area, the perimeter, and both acute angles — every number that describes the shape.
Two legs, five answers
Enter the two legs and the calculator returns the hypotenuse (√(a²+b²)), the area (½ab), the perimeter, and both acute angles in degrees at once.
Lengths share a unit, angles are degrees
The legs are unit-agnostic — the hypotenuse and perimeter come back in your unit, the area squared — while the two angles are always in degrees.
What is a right triangle calculator?
Two legs in, the whole triangle out
A right triangle calculator turns the two legs — the sides that meet at the 90° corner — into the numbers that describe the whole triangle: the hypotenuse (the long side opposite the right angle), the area, the perimeter, and the two acute angles. Each one is fixed once you know the legs, because a right angle locks the shape: there is only one triangle with those two legs. That makes the two inputs all you need for roof pitches, ramps, stair stringers, screen sizes, navigation legs, and any geometry homework where a right angle shows up.
Enter the two legs in any length unit to get the hypotenuse, area, perimeter, and both angles instantly.
A few short formulas, all built from the two legs a and b.
hypotenuse = √(a² + b²)The hypotenuse comes straight from the Pythagorean theorem: c = √(a² + b²). The area is half the product of the two legs, ½ × a × b, because the legs are the base and height of the right angle. The perimeter is just a + b + c. The angle opposite leg a is atan(a / b), and the angle opposite leg b is atan(b / a); together they always add up to 90°.
Suppose your right triangle has legs of 3 and 4.
Hypotenuse
√(3² + 4²) = √(9 + 16) = √25 = 5 — the classic 3-4-5 triangle.
Area and perimeter
½ × 3 × 4 = 6 square units, and 3 + 4 + 5 = 12 around the edge.
Angles
atan(3 / 4) ≈ 36.869898°, atan(4 / 3) ≈ 53.130102° — and 36.87 + 53.13 = 90.
The five outputs answer different practical questions. The hypotenuse (5 for legs 3 and 4) is the longest side and the one you would measure across a diagonal — a ramp's slope length, a roof rafter, a cable run; it is always longer than either leg because it sits opposite the 90° corner. The area (6 square units) is the flat space the triangle covers, handy for material or paint. The perimeter (12) is the distance all the way around, useful for fencing or trim. The two acute angles (about 36.87° and 53.13° here) describe how steep the triangle is; the single most useful insight is that they always sum to 90°, so once you know one, the other is just 90 minus it. A 3-4-5 triangle is the smallest whole-number right triangle, which is why builders use a 3-4-5 measurement to check that a corner is truly square.
The formulas are exact, but a couple of practical points are worth keeping in mind.
Only right triangles, and consistent units
These formulas assume a true right triangle — the two inputs are the legs that meet at a 90° corner, not any two sides of an arbitrary triangle. If your triangle has no right angle, use a general triangle tool instead. The legs are also unit-agnostic, so the answers are only meaningful if you keep one unit throughout: legs in centimetres give a hypotenuse and perimeter in centimetres and an area in square centimetres, never a mix. The two angles are always reported in degrees.