Triangle Calculator
Solve any triangle from sides and angles — area, perimeter and the missing values.
Enter any 3 values (at least one side). Sides a, b, c are opposite angles A, B, C.
Fill in three values to solve.
About this calculator
A triangle calculator solves a triangle from the values you know (three sides, two sides and an angle, or two angles and a side) using the law of sines and law of cosines. It returns every missing side and angle plus the area and perimeter. Enter the values you have and leave the rest blank.
Frequently asked questions
What do I need to know to solve a triangle?
Any three values that include at least one side: three sides (SSS), two sides and the included angle (SAS), two angles and a side (ASA/AAS), or two sides and a non-included angle (SSA).
How is the area calculated?
From three sides it uses Heron’s formula; with two sides and the included angle it uses ½·a·b·sin(C). Both give the same result for a valid triangle.
Results are estimates for general guidance only, not financial, medical or tax advice.