About the Law of Cosines Calculator
Solve SAS and SSS triangles using cยฒ = aยฒ + bยฒ โ 2abยทcos C.
What it is
The Law of Cosines Calculator solves for a missing side given two sides and the included angle (SAS), or for any angle given all three sides (SSS), by rearranging cยฒ = aยฒ + bยฒ โ 2abยทcos C. SSS mode first checks the triangle inequality so invalid combinations are caught before solving.
Features
SAS and SSS modes
Solve for a missing side or for any angle, depending on what you know.
Triangle inequality check
Invalid SSS combinations are flagged with a plain-English explanation.
Step-by-step working
See the formula and substitution used for every calculation.
Area, perimeter & diagram
Every solution includes area, perimeter, and a scaled triangle diagram.