The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry.

Area of a Triangle

The area A of a triangle can be calculated in various ways. The most common one is using a side and its associated the altitude:

Replacing the altitudes in the formulas above by proper sine terms leads to the following equations:

If only one side is known, but all angles are known, then the following formulas can be used:

Further, the area can be calculated from the radius of the incircle, RI, or the circumcircle RC if either all angles or the lengths of all sides are known:

Finally, Heron's formula allows to calculate the area if only the sides are known:

Last Update: 2010-12-06