Triangle Calculator

Give this calculator three known values—all three sides, two sides and the angle between them, or two angles and the side between them—and it reconstructs the triangle in full, returning every remaining side and angle along with the area and perimeter. That completeness is what makes it practical work: an architect detailing a triangular facade panel or a surveyor mapping an irregular plot needs exactly that kind of full geometric picture.

Several classical relationships do the heavy lifting. The Law of Sines (a/sin A = b/sin B = c/sin C) and the Law of Cosines (c² = a² + b² - 2ab cos C) handle most side-and-angle combinations, and the area always comes from Heron's formula, √(s(s − a)(s − b)(s − c)) with s the semi-perimeter, once all three sides are known. The solver works through these step by step, pinning down each unknown from whichever triplet you supply.

Enter angles in degrees; there is no radians option. Three angles alone cannot fix a triangle's size, so the calculator asks for at least one side, and two angles that add up to 180 degrees or more give no result. Two sides and an angle that is not between them (SSA) is not one of the input modes, because that combination can fit two different triangles—the ambiguous case—so solve it with the Law of Sines and check both possibilities.