Area Calculator
Find the area and perimeter of common shapes, with the answer in square metres and square feet.
About this tool
Choose a shape and enter its measurements in one unit. The calculator applies the standard area formula, gives the perimeter where it can, and converts the area to square metres, hectares and square feet. Everything is worked out in your browser.
Area tells you how much flat space a shape covers: the floor you need to tile, the wall you want to paint or the lawn you plan to seed. Pick a shape, enter its measurements in millimetres, centimetres, metres, inches, feet or yards, and the calculator gives the area in square units along with the perimeter and conversions to square metres and square feet. It works in your browser and nothing is saved.
How to use the Area Calculator
- Choose the shape: rectangle, square, triangle, circle, trapezoid, parallelogram or ellipse.
- Pick the unit your measurements are in.
- Enter the measurements shown for that shape; the labels change with the shape.
- Read the area, the perimeter and the square-metre and square-foot equivalents.
Tiling a 4.2 m by 3.5 m floor
A rectangular room 4.2 m long and 3.5 m wide has an area of 4.2 × 3.5 = 14.7 m², which is about 158.2 ft². Tile suppliers usually suggest buying about 10% extra for cuts and breakages, so you would order roughly 16.2 m². The perimeter is 2 × (4.2 + 3.5) = 15.4 m, which is the length of skirting board you would need before allowing for doorways.
Area formulas for common shapes
A rectangle is length × width and a square is side × side. A triangle is half of base × height, where the height is measured at right angles to the base, not along a sloping side. A parallelogram is base × height, and a trapezoid (called a trapezium in the UK and South Africa) is half the sum of the two parallel sides × the height. A circle is π × radius², and an ellipse is π × a × b, where a and b are the half-widths along its two axes. Areas are in square units, so converting needs the square of the length factor: 1 m is 100 cm, but 1 m² is 10 000 cm². For an irregular room, split it into rectangles and triangles, work out each one and add them up.
Frequently asked questions
How do I work out square metres?
Measure the length and width in metres and multiply them. A space 5 m by 4 m is 20 m². If you measured in centimetres, divide the result by 10 000 to get square metres.
How do I find the area of an L-shaped room?
Split it into two rectangles, find the area of each and add them together. The same approach works for any shape made of rectangles and triangles.
What is the difference between area and perimeter?
Area is the space inside a shape, measured in square units such as m². Perimeter is the distance around the edge, measured in ordinary length units such as metres.
Why does the triangle not show a perimeter?
The base and height are enough for the area but not for the lengths of the two other sides, so the perimeter cannot be worked out from them.