Isosceles Triangle Calculator

What Is an Isosceles Triangle Calculator?

An Isosceles Triangle Calculator is a geometry tool that helps you determine missing measurements of an isosceles triangle. An isosceles triangle has two equal sides and two equal base angles.

The calculator can determine the equal side, base, height, area, perimeter, base angles, and apex angle when enough measurements are provided.

This tool is useful for students, teachers, engineers, designers, and anyone who needs to solve triangle measurements quickly without performing the calculations manually.

How to Use the Isosceles Triangle Calculator

Choose the calculation method that matches the measurements available to you. Enter the values and select the calculate button to solve the triangle.

Isosceles Triangle Formulas

When the equal side length and base are known, the height can be found by dividing the triangle into two right triangles.

Once the height is known, the area can be calculated using the standard triangle area formula.

The perimeter is the sum of all three sides.

Properties of an Isosceles Triangle

The defining property of an isosceles triangle is that two of its sides have equal lengths. Because of this symmetry, the angles opposite those equal sides are also equal.

The altitude drawn from the apex to the base is especially useful because it bisects the base and the apex angle. It also creates two congruent right triangles.

The three interior angles always add up to 180 degrees. If each base angle is A, the apex angle can be found using 180° − 2A.

Isosceles Triangle Example

Suppose an isosceles triangle has two equal sides of 5 units and a base of 6 units.

Its area is therefore:

Its perimeter is:

Frequently Asked Questions