Triangle Theorems Calculator

  • Enter the lengths of Side A, Side B, and Side C of the triangle.
  • Select the unit for the side lengths from the dropdown menu.
  • Click "Calculate" to calculate various properties of the triangle.
  • View the results in the "Results" section below.
  • Results include perimeter, area, angles, triangle type, and more.
  • Check the "Calculation History" for previous calculations.
  • Click "Clear" to reset the input fields and results.
  • Click "Copy" to copy the results to the clipboard.

Calculation History

    What is a Triangle Theorems Calculator?

    A Triangle Theorems Calculator is an interactive online tool designed to simplify the calculations involving triangles and their associated theorems. It eliminates the need for manual computations and ensures accuracy in solving geometric problems.

    Key Concepts and Formulae

    The calculator leverages several fundamental theorems and formulae related to triangles, including:

    Law of Sines

    • Relates the sides of a triangle to their corresponding angles.
    • Formula: a/sin(A) = b/sin(B) = c/sin(C)

    Law of Cosines

    • Generalizes the Pythagorean Theorem for non-right triangles.
    • Formulas:
      • a² = b² + c² – 2bc cos(A)
      • b² = a² + c² – 2ac cos(B)
      • c² = a² + b² – 2ab cos(C)

    Pythagorean Theorem

    • Applies specifically to right triangles.
    • Formula: a² + b² = c² (where c is the hypotenuse)

    Triangle Angle Sum Theorem

    • States that the interior angles of a triangle always add up to 180 degrees.
    • Formula: A + B + C = 180°

    Benefits of Using the Calculator

    • Accuracy: Ensures precise results, minimizing errors inherent in manual calculations.
    • Efficiency: Saves time and effort by automating complex computations.
    • Versatility: Handles various triangle-related problems, including finding missing sides, angles, areas, and more.
    • Accessibility: Available online for free, providing a convenient tool for learners and professionals alike.
    • Educational Value: Reinforces understanding of geometric concepts and theorems through interactive exploration.

    Interesting Facts

    • The Law of Sines has been attributed to ancient mathematicians like Ptolemy and Islamic scholars.
    • The Pythagorean Theorem is named after Pythagoras, but its roots date back to earlier civilizations.
    • A triangle with two equal angles is called an isosceles triangle, while one with three equal angles is known as an equilateral triangle.
    • The longest side of a triangle is always opposite the largest angle, and vice versa.


    The Triangle Theorems Calculator serves as a valuable resource for students, teachers, engineers, architects, and anyone working with geometric calculations. It simplifies complex triangle-related problems, promotes accuracy, and enhances understanding of fundamental geometric concepts.


    • “Geometry for Enjoyment and Challenge” by Richard Rhoad, George Milauskas, and Robert Whipple
    • “Trigonometry” by Charles P. McKeague and Mark D. Turner
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