Isosceles triangle calculator

Height of an isosceles triangle = √(equal side² − (base ÷ 2)²). Area = base × height ÷ 2.

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Equal side length

Base length

Answer

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Height of an isosceles triangle = √(equal side² − (base ÷ 2)²). Area = base × height ÷ 2.

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Formula and assumptions

The base must be positive and shorter than twice the equal side. These strict bounds exclude degenerate triangles.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Isosceles triangle calculator

Height of an isosceles triangle = √(equal side² − (base ÷ 2)²). Area = base × height ÷ 2.

The base must be positive and shorter than twice the equal side. These strict bounds exclude degenerate triangles.

Next: Basic calculator

A worked example

With equal side length = 5, base length = 6, the area is 12.

Before you use the result

The base must be positive and shorter than twice the equal side. These strict bounds exclude degenerate triangles.

Example results for equal side length

These examples use Base length: 6. They are reference calculations, not recommended settings.

Equal side length	Area
5	12
10	28.6181760425

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