About this tool
Pick a shape, enter its dimensions, and instantly see its area and perimeter (or circumference for a circle). Triangles use Heron's formula and are checked for validity — all in your browser.
Frequently asked questions
How is the triangle area found?
From the three side lengths using Heron's formula. If the sides cannot form a triangle, you get a notice instead of a result.
What dimensions does the trapezoid need?
The two parallel sides (a and b), the two legs (c and d) and the height. Area uses the average of the parallel sides times the height.