Area calculator
Choose the shape, enter the measurements and see the area straight away, with the formula and for most shapes the perimeter too. You can enter the measurements in mm, cm, dm or m. The result is in the same unit, for example m², and is converted to other units underneath.
The side the height is perpendicular to.
Only have the diameter? Halve it.
The two parallel sides.
The perpendicular distance between the parallel sides, not the slanted side.
Half of the widest dimension.
Fill in the fields; the answer appears here straight away.
How it's worked out
How it works
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Enter the values
Type the numbers or the formula. Decimals may use a point or a comma. No idea? Click Fill in an example.
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Instant answer
The answer appears as you type, with the most important intermediate values.
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See the working
Under "How it's worked out" you see the steps, handy for checking your own calculation.
Formulas
| Shape | Area | Perimeter |
|---|---|---|
| Rectangle | length × width | 2 × (l + w) |
| Square | side × side | 4 × side |
| Triangle | ½ × base × height | – |
| Circle | π × radius² | 2 × π × radius |
| Trapezoid | ½ × (top + bottom) × height | – |
| Parallelogram | base × height | – |
| Rhombus | ½ × diagonal 1 × diagonal 2 | 4 × side |
| Ellipse | π × a × b | approximation |
A triangle, trapezoid and parallelogram have a perimeter too, but it depends on the sides and not only on the height. Do you have the three sides of a triangle, or an angle? Then the right triangle calculator helps.
Examples
- A rectangle of 8.5 by 4 metres has an area of 34 m² and a perimeter of 25 m.
- A circle with a radius of 5 cm has an area of about 78.54 cm² and a circumference of 31.42 cm. Only have the diameter? Halve it for the radius.
- A trapezoid with parallel sides of 4 and 7 metres and a height of 3 metres is ½ × 11 × 3 = 16.5 m².
- A rhombus with diagonals of 10 and 6 has an area of 30, and each side is √(5² + 3²) ≈ 5.83.
Practical tips
For walls, floors and gardens always work in one unit, and convert centimetres to metres before you compare the area with what a pack covers. A common conversion is 1 hectare = 10,000 m². For a sector, or part of a circle such as a slice of pie, use the circle sector calculator. If you need to convert an area to imperial units, see square metres to square feet. And to find out how much a room or container holds, go to the volume calculator.
Frequently asked questions
How do you work out the area of a room?
Measure the length and the width in metres and multiply them. A room of 4.2 by 3.6 metres is 15.12 m². For flooring, tiles or paint you usually add 5 to 10% for cutting waste and repairs. For a room with an alcove or an L-shape, split it into rectangles and add the areas.
What is the difference between area and perimeter?
Area is how much space a surface fills, in square units such as m². Perimeter is the length of the edge, in ordinary units such as m. A rectangle of 8 by 5 has an area of 40 m² and a perimeter of 26 m. For a fence you need the perimeter, for a floor the area.
Which height do I use for a triangle or parallelogram?
Always the perpendicular height: the distance from the base to the opposite vertex or side, measured at a right angle. For a slanted triangle or a parallelogram that is not the slanted side. Use the slanted side and the answer will be wrong.
How does the tool find the perimeter of an ellipse?
An ellipse has no simple exact formula for its perimeter. We use Ramanujan's approximation, which is very accurate for ordinary ellipses. The area π × a × b is exact.