About triangle area
This calculator finds the area of a triangle two ways: from the base and height (½ × base × height), or from the three side lengths using Heron's formula. Switch tabs to pick the method. It runs in your browser.
How Triangle Area works
How to use it
- Choose base & height, or three sides.
- Enter the measurements.
- Read the area.
The formulas
With base and height, area = ½ × base × height. With three sides a, b, c, Heron's formula gives area = √(s(s−a)(s−b)(s−c)) where s = (a+b+c)/2. The three sides must satisfy the triangle inequality.
Common uses
- Find a triangle area from base and height
- Find area from three sides
- Help with geometry homework
- Calculate land or roof areas
- Work out a triangle from measurements
- Check the triangle inequality
- Plan triangular layouts
- Learn Heron’s formula
Frequently asked questions
How do I find a triangle area?
Use base × height ÷ 2, or three sides with Heron’s formula.
What is Heron’s formula?
area = √(s(s−a)(s−b)(s−c)) with s the semi-perimeter.
Can any three sides form a triangle?
No — each side must be less than the sum of the other two.
Is my input uploaded?
No — it calculates in your browser.
Which method should I use?
Use base/height if you know the height; otherwise use three sides.
Does it round?
Results are shown to several decimal places.
Is it free?
Yes — completely free with no sign-up.