James P. Dildine, 1999

A formula for calcualting the area of a triangle when all sides are known is attirbuted to Heron of Alexandria but it is thought to be the work of Archimedes. At any rate, the formula is as follows:

A triangle has sides a, b, and c.
After Calculating S, where S = (a+b+c)/2
The Area of a Triangle = SQRT(s*(s-a)(s-b)(s-c))
Use the Fields Below to calculate the Area of a Triangle with side lengths A,B, and C.

Heron's Formula for Calculating the Area of a Triangle



A =

B =

C =


Area of
Triangle =

S = (A+B+C)/2 =>

If you get a message that details the lengths do not fulfill the triangle inequality theorem. Recall that the triangle inequality theorem states that the SUM of TWO SIDES MUST ADD UP TO BE GREATER THAN THE LENGTH OF THE REMAINING THIRD SIDE.


A + B > C, B + C> A, and A + C>B

If these are not fulfilled then you do not have a triangle and thus cannot calculate the area of an unbounded figure.