Triangle Calculator

Solve any triangle by entering known sides and angles. Choose your known values (SSS, SAS, ASA, AAS, or HL), and this calculator finds all remaining sides, angles, area, perimeter, and classifies the triangle type using the Law of Sines and Law of Cosines.

Triangle Solver

Triangle Solving Methods

Any triangle can be fully solved if you know at least three of its six measurements (sides a, b, c and angles A, B, C — where angle A is opposite side a). The method used depends on which three values you know.

CaseMethodNotes
SSSLaw of Cosinescos A = (b²+c²−a²)/(2bc)
SASLaw of CosinesFind third side, then angles
ASALaw of SinesFind third angle: C=180−A−B
AASLaw of SinesFind third angle: C=180−A−B

Area Formula

Area (SSS via Heron's): s = (a+b+c)/2 Area = √(s(s−a)(s−b)(s−c)) Area (SAS): Area = (1/2)×a×b×sin(C) Law of Cosines: c² = a² + b² − 2ab×cos(C) Law of Sines: a/sin(A) = b/sin(B) = c/sin(C)

Frequently Asked Questions

What is the Law of Cosines?+
The Law of Cosines states: c² = a² + b² − 2ab·cos(C). It generalizes the Pythagorean theorem and is used when you know two sides and the included angle (SAS) or all three sides (SSS).
What types of triangles are there?+
By angles: acute (all angles < 90°), right (one angle = 90°), obtuse (one angle > 90°). By sides: equilateral (all sides equal), isosceles (two sides equal), scalene (all sides different).
What is Heron's formula?+
Heron's formula calculates the area of a triangle when all three sides are known. The semi-perimeter s = (a+b+c)/2, then Area = √(s(s−a)(s−b)(s−c)).

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About the Triangle Calculator

This free triangle calculator helps you get accurate results instantly without needing to work through the math manually. Whether you need a quick estimate or a precise figure, having a reliable tool on hand saves time and reduces errors compared to manual calculation.

How to Use This Calculator

  1. Enter your values in the input fields above. Each field is labeled to guide you.
  2. Double-check your inputs — results are only as accurate as the numbers you enter.
  3. Click the Calculate button to see your result instantly.
  4. Use the result for your planning, budgeting, or decision-making.

Why Accurate Calculations Matter

Small errors in math calculations can compound into significant problems. A 1% miscalculation in a budget or measurement can translate to hundreds or thousands of dollars in wasted resources, or result in having to redo work entirely. This calculator uses the standard formulas and methods to give you reliable results you can trust.

Tips for Getting the Best Results

Frequently Asked Questions

Is this calculator free? Yes — completely free with no account, login, or payment required. Use it as many times as you need.

How accurate are the results? This calculator uses the standard formulas for triangle calculations. Results are accurate for typical use cases. For specialized or high-stakes applications, consult a professional.

Does it work on mobile? Yes. This calculator is fully responsive and works on smartphones, tablets, and desktops.