Math & Geometry

Triangle Calculator

Calculate the area of any triangle.

Calculate a triangle's area using either base and height, or all three side lengths (using Heron's formula).

Enter a valid base.
Enter a valid height.

Area

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How to Use This Tool

  1. Choose your method — base & height, or three side lengths.
  2. Enter the required values.
  3. Click Calculate for the area (and perimeter, if using three sides).

Two Ways to Calculate Triangle Area

Base and Height

Area = ½ × Base × Height

This is the simplest method when you know a triangle's base and its perpendicular height.

Heron's Formula (Three Sides)

Area = √[s(s−a)(s−b)(s−c)], where s = (a+b+c) ÷ 2 (the semi-perimeter)

Heron's formula lets you calculate a triangle's area knowing only its three side lengths, without needing to know the height directly — useful when height isn't easily measured.

The Triangle Inequality

For three lengths to form a valid triangle, the sum of any two sides must be greater than the third side. This calculator checks this condition and will alert you if your three side lengths can't actually form a triangle.

Frequently Asked Questions

What if my three side lengths don't form a valid triangle?

This happens when one side is longer than the sum of the other two (violating the triangle inequality) — the calculator will alert you, since no valid triangle exists with those measurements.

Which method should I use?

Use base and height if you can measure a perpendicular height directly. Use the three-sides method (Heron's formula) when you only know the side lengths and can't easily measure height.

This calculator is provided for general informational and estimation purposes only. Results should not be treated as professional financial, tax, legal, medical, or engineering advice. Always verify critical calculations with a qualified professional or official source before making decisions.