SSS, SAS, ASA
Pick the combination of sides and angles you already know and the calculator solves for everything else.
Math calculators
Triangle Calculator
Solve any triangle - all sides, angles, area, and perimeter.
Complete guide
How to use Triangle Calculator
Choose what you know - three sides (SSS), two sides and the included angle (SAS), or two angles and the included side (ASA). The calculator solves the rest with the Law of Cosines and Law of Sines and reports the area using Heron's formula.
Angles are entered and shown in degrees. The tool validates the triangle inequality so impossible triangles are rejected.
Law of Cosines & Sines
SSS uses the Law of Cosines for the angles; SAS and ASA use a mix of both laws to find the missing sides.
Area via Heron's formula
Area = √(s(s−a)(s−b)(s−c)), where s is the semi-perimeter (a+b+c)/2.
Answers
Triangle Calculator FAQs
What does SSS mean?
Side-Side-Side - you know all three side lengths. The Law of Cosines finds the angles.
What is the Law of Cosines?
c² = a² + b² − 2ab·cos(C). It relates all three sides to one angle for non-right triangles.
How is area calculated?
Using Heron's formula: Area = √(s(s−a)(s−b)(s−c)) with s the semi-perimeter.
Are angles in degrees or radians?
Degrees. To convert: degrees = radians × (180/π).
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Methodology and examples
Triangle Calculator - Solve Sides, Angles, Area & Perimeter: formula, example, and use cases
Maintained by FormatNest. Verify assumptions and sources before using results.
Formula or method
Triangle Calculator - Solve Sides, Angles, Area & Perimeter uses the values entered in its dedicated fields, validates the inputs, and applies the calculation described in the result panel.
Best use cases
Use Triangle Calculator - Solve Sides, Angles, Area & Perimeter when you need a fast browser-based estimate, comparison, or planning result without creating an account.
Important: Check the assumptions and inputs before relying on this estimate for an important decision.
Editorial note: Review the input definitions, units and assumptions before relying on results. For corrections, contact FormatNest with your inputs and expected result.