Enter the three side lengths. Angles, area, height, and perimeter are computed from them.
Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
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Use this result
Share the current inputs or ask ChatGPT to explain the calculation in context.
What does this calculator estimate?
A triangle with base 10 and height 5 has area 1/2 x 10 x 5 = 25 square units. The angles of any triangle sum to 180 degrees; three sides give area via Heron's formula.
- Area = 1/2 x base x height; Heron's formula works from three sides (Wikipedia).
- Triangle angles always sum to 180 degrees.
- The longest side faces the largest angle.
What triangle solving covers
Triangles are the building blocks of geometry, construction, and surveying. The calculator finds area, sides, and angles from the inputs you have — base/height, three sides (Heron's formula), or side-angle combinations.
Limitations to watch for
Not every combination of inputs is valid — sides must satisfy the triangle inequality (each side < sum of the other two). Angles are in degrees. Ambiguous cases (SSA) may have two solutions.
How to use it in practice
Enter what you know and read the rest. Use it for roof pitches, land plots, and geometry problems. For right triangles, the Pythagorean tools handle the special case directly.
['Enter the known sides and/or angles.', 'The tool computes the missing values.', 'Use the area and dimensions for your project.']
How this calculator works
Formula
Solves triangles from given sides/angles: area = ½ × base × height, and via Heron's formula from three sides. Angles sum to 180°.
Worked example
A triangle with base 10 and height 5: area = ½ × 10 × 5 = 25 square units.
Assumptions to verify
- Angles are in degrees.
- Inputs satisfy the triangle inequality.
- Standard Euclidean geometry applies.
Frequently asked questions
How do I find the area of a triangle?
½ × base × height: ½ × 10 × 5 = 25 square units.
What if I only know the three sides?
Use Heron's formula — the tool handles it.
Do all triangles have 180°?
Yes — in Euclidean geometry, the three angles always sum to 180°.
What is the triangle inequality?
Each side must be shorter than the sum of the other two, or the triangle can't exist.
Can it solve right triangles?
Yes — it covers them; the Pythagorean calculator is the faster special case.
What units does it use?
Any consistent unit — the area comes out in the same unit squared.
What is an ambiguous case?
Side-side-angle data can produce two valid triangles — a known trap in trigonometry.
Cite this tool
BoringToolsKit. “Triangle Calculator.” boringtoolskit.com/triangle-calculator/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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