Math Calculators
Triangle Calculator
Solve a triangle from its three sides.
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About the Triangle Calculator
Enter the three side lengths of a triangle and the calculator solves it completely: all three interior angles (via the law of cosines), the area (via Heron's formula), and the perimeter. It also checks the triangle inequality so you know whether the sides can actually form a triangle. Perfect for geometry, trigonometry, and design work.
How to use the Triangle Calculator
- 01Enter your three side lengths (SSS).
- 02Read the result instantly — it recalculates as you type.
- 03Adjust the numbers to model different scenarios.
Frequently asked questions
How do you find a triangle's area from its sides?
Heron's formula: with s = (a+b+c)/2, area = √(s(s−a)(s−b)(s−c)). This tool uses it automatically.
Can any three lengths make a triangle?
Only if each side is shorter than the sum of the other two (the triangle inequality). The calculator flags invalid sets.