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Heron's Formula Triangle Calculator

Triangle area from three side lengths.

Area
6.0000
square units
Perimeter
12.0000
Semi-perimeter
6.0000

Interior angles

  • Angle A (opposite a)
    36.87°
  • Angle B (opposite b)
    53.13°
  • Angle C (opposite c)
    90.00°

Area uses Heron's formula. Angles come from the law of cosines.

About

Heron's formula gives the area of any triangle when you know all three side lengths. No need for the height. Useful when you've measured a plot of land, a sail, or any non-right triangle.

How to use

  1. Enter the three side lengths.
  2. See the area, semi-perimeter, and angle measures.

FAQ

What if my sides don't form a valid triangle?+

Triangle inequality: the sum of any two sides must be greater than the third. If they don't, no triangle exists. The tool flags this.