basic

Law of Cosines: Unknown Side or Angle Calculator

c² = a² + b² − 2ab·cos C — any triangle.

Applies the law of cosines c² = a² + b² − 2ab·cos C to find an unknown side or angle in any triangle. Also computes the area using Heron's formula.

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

°

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

c² = a² + b² − 2ab·cos C

In depth

Applies the law of cosines c² = a² + b² − 2ab·cos C to find an unknown side or angle in any triangle. Also computes the area using Heron's formula.