Area Calculator

1. Select the shape. Choose from rectangle, square, circle, triangle, trapezoid, ellipse, parallelogram, or circle sector. The required dimension inputs update automatically for each shape.
2. Enter a unit (optional). Type your unit (m, ft, cm, in, etc.) and the result will display in square units. Leaving it blank still gives the correct numerical answer.
3. Enter the dimensions. For a rectangle, enter length and width. For a circle, enter the radius (not diameter). For a triangle, enter base and perpendicular height, not the slant side.
4. Read the results. The calculator shows area and perimeter or circumference where applicable, plus the formula used. The reference table at the bottom shows all 8 shape formulas at a glance.

Real example: a circular garden with radius 7 feet has area = π x 7² = 153.94 ft². A rectangular lawn 40 ft x 25 ft = 1,000 ft².

All area calculations use the same fundamental idea: the amount of 2D space enclosed by a boundary. Here are the formulas with worked examples:

For the sector, convert degrees to radians first: radians = degrees × π/180. A 90-degree sector = 1.5708 radians. The perimeter of a sector = 2r + arc length, where arc length = rθ.