Triangle Calculator
Calculate the area and perimeter of any triangle from its three side lengths.
Calculate
Enter your values below.
Result
Area
0
Perimeter
0
Formula used
Area is found using Heron's formula: with s = (a+b+c)/2, Area = √(s(s−a)(s−b)(s−c)).
Example: Sides 3, 4, 5 → area = 6, perimeter = 12.
How to use this calculator
- Enter Side a, Side b, Side c.
- Press Calculate to see your result instantly.
FAQ
Frequently asked questions
What is Heron's formula?
A way to calculate a triangle's area using only its three side lengths, without needing the height.
What if the sides can't form a triangle?
The calculator checks the triangle inequality (each side must be less than the sum of the other two) and shows an error if it fails.
Does this work for right triangles too?
Yes — Heron's formula works for any valid triangle, including right triangles.
How is perimeter calculated?
Simply the sum of all three sides: a + b + c.