Right Triangle Calculator

How to use

1. 1Pick a solver mode: Two sides known, or One side and one acute angle.
2. 2If you picked Two sides, choose which pair (a and b, a and c, or b and c) and enter their values.
3. 3If you picked Side and angle, choose which side (a, b, or c) and which acute angle (A or B), then enter their values. The angle is in degrees, strictly between 0 and 90.
4. 4Optional: click a Pythagorean triple chip (3-4-5, 5-12-13, 8-15-17, 7-24-25, 9-40-41) to fill the active inputs with a worked example.
5. 5Read the full solution: all three sides, both acute angles in degrees and radians, perimeter, area, altitude to the hypotenuse, inradius, circumradius, and sin/cos/tan for both acute angles.
6. 6Click Copy on any row to copy that single value, or use Copy full report to copy the entire breakdown including the step-by-step equations.

About this tool

Right Triangle Calculator solves any right triangle when you know any two of its measurements. Enter two sides and the tool applies the Pythagorean theorem (a^2 + b^2 = c^2) to find the third side, then uses atan2 to recover the two acute angles. Enter one side and one acute angle, and it uses the trigonometric definitions (sin, cos, tan) to derive the missing side and the other angle. Sides are labeled a (the vertical leg), b (the horizontal leg), and c (the hypotenuse). Angles are labeled A (opposite side a), B (opposite side b), and C (the right angle, always 90 degrees). The output covers everything a typical homework problem, construction layout, woodworking cut, surveying calculation, screen-fitting estimate, or geometry refresh might need: all three sides, both acute angles in degrees and radians, the perimeter, the area, the altitude from the right angle to the hypotenuse, the inradius and circumradius, and the sin, cos, and tan values for both acute angles. A scaled SVG preview redraws the triangle in real time as you type so you can sanity-check the proportions and confirm which leg is which. A step-by-step breakdown shows the exact equations used, with the substituted numbers, so the answer is auditable instead of opaque. Quick-fill buttons load the well-known integer-side Pythagorean triples (3-4-5, 5-12-13, 8-15-17, 7-24-25, 9-40-41) when you just want a sanity check or a worked example. The tool validates inputs and refuses geometrically impossible combinations: a hypotenuse shorter than a leg returns a clear explanation, and an acute angle of 90 degrees or more is rejected because that would make the triangle degenerate. All math runs locally in your browser with no upload, no server call, and no analytics, so the values you enter for school assignments, construction estimates, or design work stay on your device.

Free to use. Works in your browser. No signup, no login.