Isosceles Triangles Calculator

Isosceles Triangles Calculator

  • Enter the base and side lengths of the isosceles triangle.
  • You can optionally input the height directly or calculate it.
  • Select the units for measurements and angle units (degrees or radians).
  • Choose the triangle style (default, outlined, or filled).
  • Check the boxes to calculate inradius and circumradius if needed.
  • Click "Calculate" to get the results.
  • Use "Clear Results" to reset the results and "Copy Results" to copy to the clipboard.
  • Click "Save Diagram as Image" to save the triangle diagram as an image.


Isosceles triangles are a fundamental concept in geometry, characterized by having two sides of equal length and two equal angles. These triangles have numerous real-world applications, from construction to art, making them a critical topic for students and professionals alike. To aid in the study and application of isosceles triangles, the Isosceles Triangles Calculator is a valuable tool.

The Concept of Isosceles Triangles

An isosceles triangle is a polygon with two sides of equal length, called legs, and two angles of equal measure, which are opposite the equal sides. The third angle, opposite the base, is referred to as the vertex angle. Isosceles triangles can be classified based on the measurement of the vertex angle:

  1. Acute Isosceles Triangle: All angles are less than 90 degrees.
  2. Right Isosceles Triangle: One angle is 90 degrees.
  3. Obtuse Isosceles Triangle: One angle is greater than 90 degrees.

Formulae for Isosceles Triangles

Understanding the properties of isosceles triangles requires familiarity with several formulae:

Pythagorean Theorem

In a right isosceles triangle, where one angle is 90 degrees, the Pythagorean theorem is applicable:

  • c^2 = a^2 + b^2 Where:
  • c is the length of the hypotenuse (the side opposite the right angle).
  • a and b are the lengths of the two equal legs.


The perimeter (P) of an isosceles triangle can be calculated as:

  • P = a + b + c Where:
  • a and b are the lengths of the two equal legs.
  • c is the length of the base (opposite the vertex angle).


The area (A) of an isosceles triangle can be determined using the following formula:

  • A = 0.5 * b * h Where:
  • b is the length of the base (the side opposite the vertex angle).
  • h is the height, which can be calculated using the Pythagorean theorem:
    • h = √(a^2 – (b^2 / 4))

Example Calculations

Let’s consider an example to demonstrate the application of these formulae. Suppose we have an isosceles triangle with legs of length 6 units each and a base of 8 units.

Pythagorean Theorem:

  • c^2 = 6^2 + 6^2
  • c^2 = 36 + 36
  • c^2 = 72
  • c = √72 ≈ 8.49 units


  • P = 6 + 6 + 8 = 20 units


  • h = √(6^2 – (8^2 / 4))
  • h = √(36 – 16)
  • h = √20 ≈ 4.47 units
  • A = 0.5 * 8 * 4.47 ≈ 17.88 square units

Real-World Use Cases

Isosceles triangles find applications in various real-world scenarios:


In construction, isosceles triangles are used to create stable structures. Roof trusses, for example, utilize isosceles triangles to distribute weight evenly.

Art and Design

Artists and designers use isosceles triangles to create visually pleasing compositions. The symmetry of isosceles triangles can be found in architectural details, logos, and patterns.


Navigation tools, such as compasses and sextants, rely on isosceles triangles to calculate distances and angles, helping sailors and explorers find their way.


Engineers use isosceles triangles in the design of bridges and supports, ensuring structural integrity and load-bearing capacity.


The Isosceles Triangles Calculator is a valuable tool for students, educators, and professionals dealing with geometry and its real-world applications. Understanding the concept of isosceles triangles and the associated formulae is crucial for solving problems in various fields, from mathematics and engineering to art and construction.

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