What is an area calculator?
An area calculator finds the amount of flat surface inside a two-dimensional shape. It can help with room plans, gardens, flooring, paint estimates, fabric, schoolwork and many everyday measurements. Choose a shape, enter its dimensions in one consistent unit and the calculator displays the resulting area in squared metres, centimetres, feet or inches.
This calculator handles four common shapes: rectangles, circles, triangles and trapezoids. It performs the arithmetic in your browser, so the measurements you enter stay on your device. The unit selector does not convert a measurement; it labels both the dimensions and the answer. For example, dimensions entered in feet produce an answer in square feet.
How to calculate an area
- Select the shape you want to measure.
- Pick the unit used for every dimension.
- Enter each required length, radius, base or height.
- Read the area and the formula used below the result.
For a rectangular room that is 10 metres long and 5 metres wide, the area is 50 square metres. If the same figures were feet, the answer would be 50 square feet instead. Keep every measurement in the same unit before calculating. Convert mixed measurements first, such as a length in feet and a width in inches.
Area formulas used by this tool
For a rectangle, area equals length multiplied by width. A square uses the same formula because its length and width match. For a circle, area equals pi multiplied by the radius squared; the radius is the distance from the centre to the edge, not the diameter. For a triangle, area equals the base times the perpendicular height divided by two.
A trapezoid has two parallel bases of different lengths. Its area equals the sum of the top and bottom bases multiplied by the height, then divided by two. The height must be the straight perpendicular distance between those parallel bases. Using a sloped side instead can give the wrong answer.
Why correct units matter
Area is always expressed in square units because it describes a surface, not a single length. One square metre is very different from one square foot, so use the right unit before ordering material or estimating cost. Round only after the calculation when practical: flooring, paint and similar projects may also need an allowance for cuts, waste, overlaps or uneven spaces. Measure carefully and follow supplier guidance for a final quantity estimate.