How triangle calculator works
A triangle is fully determined by its three side lengths, as long as they satisfy the triangle inequality: the sum of any two sides must exceed the third. Given valid sides a, b, and c, the area follows from Heron's formula using the semi-perimeter s = (a+b+c)/2: area = √(s(s−a)(s−b)(s−c)).
The three angles come from the law of cosines: cos A = (b² + c² − a²) / (2bc), and similarly for B and C, converted from radians to degrees. The largest angle classifies the triangle: a right triangle has a 90° angle, an obtuse triangle has one angle above 90°, and an acute triangle has all angles below 90°.
Enter the three side lengths. The calculator validates that they form a triangle, computes the area and perimeter, finds all three angles, and classifies the triangle as equilateral (all sides equal), isosceles (two equal), or scalene (all different), and as acute, right, or obtuse.