Area Calculator

Rectangle: length. Square: side. Triangle: base. Circle: radius. Trapezoid: parallel side a. Parallelogram: base. Ellipse: semi-major axis.
Rectangle: width. Ellipse: semi-minor axis. Trapezoid: second parallel side b. Not used for square, circle, triangle (height), parallelogram (height).
Used for: triangle, trapezoid, parallelogram. Not used for rectangle, square, circle, ellipse.
Math

The Area Calculator finds the area of common shapes — rectangle, square, triangle, circle, trapezoid, parallelogram, and ellipse — from their dimensions. The formulas used are: Rectangle: l×w. Square: s². Triangle: ½bh. Circle: πr². Trapezoid: ½(a+b)h. Parallelogram: bh. Ellipse: πab.

Formula

Rectangle: l×w. Square: s². Triangle: ½bh. Circle: πr². Trapezoid: ½(a+b)h. Parallelogram: bh. Ellipse: πab.
  • The Area Calculator updates instantly as you change the shape or its dimensions.
  • Formula: Rectangle: l×w. Square: s². Triangle: ½bh. Circle: πr². Trapezoid: ½(a+b)h. Parallelogram: bh. Ellipse: πab.
  • Input definitions: • Side a: length / radius / base / semi-major axis, depending on the shape • Side b: width / semi-minor axis / second parallel side • Height: used for triangle, trapezoid, and parallelogram
  • Pick the shape first; only the relevant inputs are used for that shape's formula.
  • All dimensions must share the same unit, and the area comes out in that unit squared.
  • For rectangles, squares, and circles the calculator also shows perimeter or circumference.

Example Calculation

Inputs
  • Side a (length / radius / base / semi-major axis): 8
  • Side b (width / semi-minor axis / second parallel side): 5
  • Height (h): 4

For a rectangle with side a = 8 and side b = 5, area = 8 × 5 = 40 square units. Switch the shape to triangle and the same a = 8 with height 4 gives ½ × 8 × 4 = 16.

Frequently asked questions

Which shapes does this calculator support?
Rectangle, square, triangle, circle, trapezoid, parallelogram, and ellipse. Choose the shape and enter its dimensions.
Which inputs are used for each shape?
Side a is the length, radius, base, or semi-major axis; side b is the width, semi-minor axis, or second parallel side; height is used for triangle, trapezoid, and parallelogram.
What units should I use?
Use the same length unit for every dimension. The area is then in that unit squared (e.g. m²).
Does it also give perimeter?
For rectangles and squares it shows the perimeter, and for circles it shows the circumference.
How is the area of an ellipse found?
Area = π × semi-major axis × semi-minor axis (πab), entered as side a and side b.
How can I verify the calculation manually?
Apply the shape's formula shown in the result help text and compare with your own arithmetic.
What if my shape is irregular?
Split it into these basic shapes, find each area, and add them together.

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