Interactive calculator
Area calculator
Pick a shape and enter dimensions.
Area-
Formula used-
About this tool
The Area Calculator computes the area of common 2D shapes: rectangle, square, circle, triangle, trapezoid, parallelogram, and ellipse. Select the shape, enter dimensions, and get the area with the formula shown.
What this area calculator does
The area of a shape is the amount of flat surface it covers, measured in square units. This tool computes that area for the six shapes you meet most often (rectangle, triangle, circle, trapezoid, parallelogram, and ellipse): you pick the shape, type its dimensions, and it applies the right formula and shows which one it used. Everything runs in your browser, so your measurements stay on your device.
Area is one of the most practical numbers in daily life. You need it to buy the right amount of paint, flooring, turf, fabric, or fertiliser, to price land, and to size anything that has to fit a surface. Getting it right saves both money and a second trip to the shop.
How it works: the formulas
Each shape has its own area formula. The calculator selects the matching one from your dropdown choice and the dimensions you enter.
Rectangle / square A = width x height Triangle A = (1/2) x base x height Circle A = pi x radius^2 Trapezoid A = (1/2) x (base1 + base2) x height Parallelogram A = base x height Ellipse A = pi x semi_axis_a x semi_axis_b
Two ideas tie these together. For straight-sided shapes the area is always a base multiplied by a perpendicular height (the triangle and trapezoid just carry a factor for the slanted parts). For round shapes the constant pi (about 3.14159) links a radius to the curved area, and an ellipse is simply a circle stretched along two different half-widths.
Worked example: a trapezoidal garden bed
Imagine a raised bed shaped like a trapezoid: the two parallel sides are 6 m and 10 m, and the perpendicular distance between them is 4 m. You want the area to order topsoil.
- Identify the parallel sides: base1 = 6 m, base2 = 10 m.
- Identify the height: the perpendicular gap, h = 4 m (not the slanted edge).
- Average the bases: (6 + 10) / 2 = 8 m.
- Multiply by the height: 8 x 4 = 32.
- Read the units: dimensions were in metres, so the area is 32 square metres.
Result: 32 square metres. If your topsoil supplier sells by volume, multiply this area by the bed depth (say 0.2 m) to get 6.4 cubic metres.
Where area calculations show up
Area is the hidden input behind a surprising number of everyday quotes and purchases. Knowing how to compute it quickly lets you check a contractor's figure or estimate a job before you call anyone.
- Paint and wallpaper: wall area divided by the coverage printed on the tin gives the number of litres or rolls, usually with a second coat in mind.
- Flooring and tiling: room area plus a cutting allowance tells you how many boxes of tiles, planks, or square metres of carpet to order.
- Lawns and gardens: turf, seed, and fertiliser are all sold per square metre, so the plot area sets the quantity directly.
- Real estate: floor area in square feet or square metres drives both price comparisons and rental yields.
- Fabric and craft: upholstery and sewing projects price material by area once you account for the pattern repeat.
Area formula reference
The dimension labels match the inputs in the calculator above.
| Shape | Formula | Inputs needed | Notes |
|---|---|---|---|
| Square | A = side^2 | one side | Special rectangle, all sides equal |
| Rectangle | A = w x h | width, height | Most common case |
| Triangle | A = (1/2) b h | base, height | Height is perpendicular to base |
| Parallelogram | A = b h | base, height | Height, not the slanted side |
| Trapezoid | A = (1/2)(b1 + b2) h | two bases, height | Bases are the parallel sides |
| Circle | A = pi r^2 | radius | Use radius, not diameter |
| Ellipse | A = pi a b | two semi-axes | a and b are half-widths |
Common pitfalls
- Using the slanted side as the height. For triangles, trapezoids, and parallelograms the height is the perpendicular distance, which is shorter than the sloping edge.
- Entering diameter instead of radius. Circle and ellipse formulas use the radius (half the width). Entering the full diameter makes a circle four times too large.
- Mixing units within one shape. Convert everything to a single unit first, otherwise the product is meaningless.
- Confusing area with perimeter. Paint and flooring need area (square units); fencing and trim need perimeter (length units).
- Forgetting waste and offcuts. Real projects need 5 to 15 percent extra material for cuts, pattern matching, and breakage, so add a margin to the bare area.
- Treating an irregular plot as one rectangle. Split odd shapes into rectangles and triangles, find each area, and add them rather than guessing an average.
Related tools
Frequently asked questions
How do you calculate the area of a trapezoid?
Area = (1/2) x (base1 + base2) x height, where the two bases are the parallel sides. A trapezoid with parallel sides of 6 cm and 10 cm and a height of 4 cm has Area = (1/2) x 16 x 4 = 32 square cm.
What is the difference between area and perimeter?
Area measures the space inside a shape and is expressed in square units, such as square metres. Perimeter measures the distance around the edge and is expressed in plain length units, such as metres. Two shapes can share a perimeter but have very different areas.
What units does the area come out in?
Whatever unit you enter, squared. If your dimensions are in metres the area is in square metres, and if they are in feet the area is in square feet. Always enter every dimension of one shape in the same unit, then convert at the end if you need different units.
How do I find the area of an irregular shape?
Split it into simple shapes you can measure, such as rectangles and triangles, compute each area with this tool, and add them up. For shapes with a curved edge, approximate the curve with a circle, ellipse, or a series of thin trapezoids.
Why is the circle area so much larger than I expected?
Because area grows with the square of the radius: A = pi r^2. Doubling the radius quadruples the area. A common mistake is entering the diameter where the radius is asked, which makes the result four times too big.