What is the Triangle Calculator?
An online math tool on LeCalculators that solves triangle calculator problems with clear numeric results for study and everyday use.
Triangle Calculator
Pick SSS, SAS, or ASA, enter the known sides and angles, and get the full triangle solution.
Choose a mode and enter known parts
SSS needs three sides. SAS needs two sides and the included angle. ASA needs two angles and the included side.
About this calculator
How to use Triangle Calculator, plus the formulas and logic behind the results.
Tool description
Combines Law of Cosines and Law of Sines to complete the triangle and Heron’s formula for area when all sides are known.
How to use
- Review the input fields and choose degrees or radians when asked.
- Enter the known values using consistent units.
- Select Calculate to view results.
- Adjust inputs and recalculate as needed.
Formulas & reference
c² = a² + b² − 2ab cos C (SAS)cos A = (b² + c² − a²) / (2bc) (SSS)a / sin A = b / sin B (ASA completion)Area = √[s(s−a)(s−b)(s−c)]
Trig tips
- Confirm angle mode (degrees vs radians) before evaluating sin, cos, tan.
- Right-triangle tools assume a 90° angle between legs a and b.
- Triangle inequality: each side must be shorter than the sum of the other two.
Calculation logic
Dispatches by mode to SSS, SAS, or ASA solvers. Angles are converted with the selected angle mode. Invalid or degenerate triangles return an error.
Educational calculator. Floating-point rounding may differ slightly from textbook answers.
Triangle Calculator FAQ
Common questions about this calculator and how to use the results.
Do I use degrees or radians?
Many trig tools include an angle mode selector. Match the mode to how your angle is written—degrees (°) or radians.
Why is my answer undefined or invalid?
Trig functions have domain limits (for example arcsin needs −1…1). Triangle tools also reject sides that violate the triangle inequality.
How precise are the results?
Results use floating-point math and are rounded for display with mathFormat. Tiny rounding differences vs hand calculation are normal.
Is this calculator free?
Yes. LeCalculators trigonometry tools are free to use in your browser with guides and FAQs on each page.
Can I use this for homework?
Yes—use it to check work. Always show your own steps when your teacher requires a written solution.