How to use this calculator
- Choose a shape.
- Enter its dimensions in any consistent unit (all in cm, or all in feet, for example).
- The area is in square units of what you entered.
Formula
Each shape has its own formula.
Rectangle: A = l × w
Circle: A = πr², C = 2πr
Triangle: A = ½ × b × h
Trapezoid: A = ½(a + b) × h
Ellipse: A = πab
Sector: A = (θ/360) × πr²
Regular n-gon: A = n s² / (4 tan(π/n))
Example
- Circle with radius 3: A = π × 9 ≈ 28.274 square units.
- Circumference = 2π × 3 ≈ 18.850 units.
Frequently asked questions
How do I find the area of an irregular shape?
Split it into rectangles, triangles and circles, calculate each area, and add them together (or subtract cut-outs).
How do I convert square feet to square meters?
1 square foot = 0.09290304 m². Use the area converter for any area units.
Why is the ellipse perimeter approximate?
An ellipse's perimeter has no simple exact formula. Ramanujan's approximation used here is accurate to within a tiny fraction of a percent.