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Isosceles Triangle Calculator.

Calculate height, area, perimeter, and angles from base and equal side.

On-device calculationNo signup
01

Set your values

Results update as you type.

Height: 4 units

Height

0.000000units
Area: 12 units²

Area

0.000000units²
Perimeter: 16 units

Perimeter

0.000000units
Vertex angle: 73.739795 °

Vertex angle

0.000000°
Base angle: 53.130102 °

Base angle

0.000000°

Results update automatically as you type.

Use Cases

Geometry homework and math practice

Quickly verify your manual calculations for isosceles triangle properties, such as height, area, and angles, to ensure accuracy.

Example: Check the height of a triangle with base 10 and equal side 13.

Design and construction planning

Determine dimensions for roof trusses, gables, or other structures that use isosceles triangle shapes.

Example: Calculate the area of a triangular sign with base 4 ft and equal sides 5 ft.

Frequently Asked Questions

How do I use the isosceles triangle calculator?
Enter the length of the base and the length of one of the equal sides in the provided fields. The calculator will compute the height, area, perimeter, and all angles of the isosceles triangle.
What units should I use for the base and equal side?
You can use any consistent unit of length (e.g., inches, centimeters, meters). The calculator will output results in the same unit for lengths and square units for area.
Can this calculator handle any base and equal side lengths?
The calculator works for any positive numbers where the equal side is greater than half the base. If the equal side is too short, the triangle cannot exist, and the calculator may not provide valid results.

Tips & Common Mistakes

Tips

  • Ensure the equal side is longer than half the base; otherwise, the triangle is impossible.
  • Use the same unit for both base and equal side to get correct results.
  • The height is measured perpendicular from the base to the apex, not along the equal side.
  • Angles are automatically calculated; the base angles are equal, and the apex angle is the remaining.

Common Mistakes to Avoid

  • Entering the base and equal side in different units, leading to incorrect calculations.
  • Assuming the equal side is the height; the height is always less than the equal side.
  • Using a base that is too long relative to the equal side, resulting in an invalid triangle.

Last updated: August 13, 2026