Toolstia / Area calculator
Area calculator
Pick a shape, enter its measurements and get the area and, where it applies, the perimeter. Twelve common shapes are covered, including a triangle from three sides using Heron’s formula and a regular polygon with any number of sides.
Use the same unit for every measurement. Areas come out in square units of that unit and volumes in cubic units.
How it works
- Choose the shape.
- Enter the measurements in any one unit.
- Read the area and perimeter.
Formulas used
Rectangle: l × w. Triangle: ½ × base × height. Circle: πr². Trapezoid: ½(a + b)h. Ellipse: πab. Regular polygon: n s² ÷ (4 tan(π/n)). Sector: ½r²θ.
Heron’s formula
With three sides a, b, c and s as half the perimeter, the area is √(s(s−a)(s−b)(s−c)). The tool also warns when three sides cannot form a triangle.
Ellipse perimeter
There is no simple exact formula, so the tool uses Ramanujan’s approximation, which is accurate to a tiny fraction of a percent for most ellipses.
Units
Use the same unit for every length. The area is in that unit squared.
Questions
Does it convert units?
No. Whatever unit you use for lengths, the area is in square units of the same unit.
What angle unit does the sector use?
Degrees.
Is anything uploaded?
No. Your input stays in your browser and is never sent anywhere.