Isosceles Triangle Calculator

Find the height, area and perimeter of an isosceles triangle given its base and equal side length.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

An isosceles triangle has two sides of equal length, and knowing just the base and that equal side length is enough to find everything else: the height splits the base exactly in half, forming a right triangle that the Pythagorean theorem solves, and the area and perimeter follow directly from there.

Carpenters and roofers use isosceles-triangle math when framing a gable end or a triangular roof truss, since the two equal rafters and the span between them form exactly this shape. It also comes up constantly in classroom geometry, where the isosceles triangle is one of the first special triangles students learn to solve without needing every side given directly.

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