Triangle Calculator
Solve a triangle's missing side, angles, and area from two sides and the included angle.
Enter any 3 values (at least one side) to solve the triangle. Angles in degrees.
Side c & area
Enter sides a, b and angle C
This solver uses the Law of Cosines for the SAS (side-angle-side) case, the most common triangle lookup.
Related calculators
Solving a triangle with the Law of Cosines
Given two sides and the angle between them (the SAS case), the Law of Cosines finds the third side: c² = a² + b² − 2ab·cos(C). From there, the Law of Sines finds the remaining angles, and the standard area formula (½ab·sin C) gives the triangle's area.
Frequently asked questions
- What if I only know three sides (SSS)?
- This version solves the SAS case; for SSS, the Law of Cosines is rearranged to solve for an angle first — a variant we may add in future.
- Does this work for right triangles?
- Yes, a 90° angle for C is a valid input and the calculator will correctly reduce to the Pythagorean theorem.