An 8 m by 5 m rectangle has an area of 40 m², which is 430.556 square feet. Its perimeter is 26 m.
What this calculates
Choose a shape, a unit and its dimensions. This works out the area in that unit squared, the perimeter or circumference where the dimensions fix it, and the area in square metres and square feet. It covers the rectangle, square, triangle, circle, trapezoid, parallelogram and ellipse. To convert between units of area alone, use the area converter.
The formula
Rectangle
A = length × widthTriangle
A = ½ × base × heightCircle
A = π × r²Trapezoid
A = ½ × (a + b) × heightParallelogram
A = base × heightEllipse
A = π × r₁ × r₂The perimeter is 2 × (length + width) for a rectangle, 4 × side for a square and 2πr for a circle.
Worked example
A circle of radius 5 m has an area of π × 25 = 78.5398 m² and a circumference of 31.4159 m.
When to use it, and the mistakes to avoid
Use it for flooring, paint, turf, a garden bed, a plot of land, a tablecloth or a sheet of material.
The mistakes that cost the most:
- Using a slanted side as the height. The height is perpendicular to the base.
- Using the diameter as the radius. The radius is half the diameter.
- Mixing units. Measure every side in the same unit before you start.
- Reading square units as plain units. 10 m² is ten metre-squares, not 10 metres.
- Forgetting waste. Buy 5% to 10% more flooring or paint than the area.
FAQ
How do I calculate the area of a rectangle?
Multiply the length by the width. An 8 m by 5 m rectangle has an area of 8 × 5 = 40 square metres. A square is a rectangle with equal sides, so its area is the side squared.
What is the area of a circle?
π times the radius squared. With a radius of 5 m, the area is π × 25 = 78.54 m². The radius is half the width across the middle. If you know the diameter, halve it first.
Why does the triangle need a height, not a side?
The area is half the base times the height, where the height is the straight, perpendicular distance from the base to the opposite corner. A slanted side is longer than the height, so using it overstates the area. The same goes for a parallelogram and a trapezoid.
How do I get the area of a trapezoid?
Add the two parallel sides, halve the total, and multiply by the height between them. With parallel sides of 6 and 10 and a height of 4, the area is ½ × 16 × 4 = 32.
What unit is the area in?
The unit you choose, squared: metres give square metres, feet give square feet. The result is also shown in square metres and square feet, so you can compare. A square foot is 0.09290304 square metres exactly.