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Area calculator with formulas and working

Choose your shape and enter the measurements to find the area. The calculator shows the working and handles measurements in mm, cm and m as well as inches, feet and yards.

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One side of the rectangle.

The other side of the rectangle, perpendicular to the length.

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Worked example
  • Shape: Rectangle
  • Length: 12 m
  • Width: 10 m

Result

Area

120 m²

Working

  1. A = l × b
    12 m × 10 m = 120 m²

Which measurements do you need for the area?

Area tells you how large a surface is. It is useful when you measure a floor, a piece of fabric or a shape in a math problem. The result is given in square units, for example m² or cm², because the calculation is about a surface.

A rectangle needs length and width: A = l × b. For a square the sides are equal, so the formula is A = a². A triangle is calculated with A = b × h / 2. The height must be perpendicular to the base. If you know all three sides instead, you can choose a triangle with three sides, which uses Heron's formula.

Area of round and slanted shapes

For a circle the formula is A = π × r². The radius runs from the center to the edge. You can also choose to enter the diameter. An ellipse is calculated with A = π × a × b, where a and b are the semi-axes.

A parallelogram uses A = b × h. A trapezoid uses A = (a + b) × h / 2, where a and b are the parallel sides. Measure the height perpendicular between the sides, so a slanted side length is not used as the height.

Examples of area calculations

A rectangle of 12 m by 10 m gives 12 m × 10 m = 120 m². For a triangle with a base of 6 m and a height of 4 m, the calculation is 6 m × 4 m / 2 = 24 m² / 2 = 12 m².