Area Calculator
Twelve shapes covering area, perimeter and every unit including acres
Every length uses the one unit you pick, and the results are converted into square feet, square metres, acres and hectares for you. Decimals are fine: a 7½-foot wall is 7.5.
Full breakdown & every unit
| Item | Value | Detail |
|---|
How to Use
- 1Pick your shape and only the fields it needs appear.
- 2Choose the unit you measured in, then enter every length in that unit.
- 3Read the area, with the perimeter on the line beneath it.
- 4Open the breakdown for square metres, square feet, acres and hectares.
The Formulas
- RectangleA = length × width
- TriangleA = ½ × base × height
- CircleA = π r²
- TrapezoidA = ½ (b₁ + b₂) h
- EllipseA = π a b
- Regular polygonA = n s² ÷ 4 tan(π/n)
Quick Examples
Tap an example to load it above.
Everything about the Area Calculator
Twelve shapes, real units, and the perimeter nobody else gives you.
Area is how much flat space a shape covers, measured in square units. This area calculator handles twelve two-dimensional shapes, from a plain rectangle to a sector, a ring, a regular polygon and an L-shaped room, and reports the perimeter alongside the area, because the moment you know how much floor to cover you usually need to know how much edging to buy.
It also does the unit conversion for you. Enter feet and you get square feet, square metres, acres and hectares at the same time, so working out whether a plot is "about half an acre" takes no second calculator.
Areas do not scale the way lengths do. Doubling every side of a shape multiplies its area by four, not two. This is also why unit conversion trips people up: 1 metre is about 3.28 feet, but 1 square metre is about 10.76 square feet, because the ratio gets squared.
Which shape should I pick?
| You have | Choose | Perimeter? |
|---|---|---|
| A room, wall, lawn or plot | Rectangle or square | Yes |
| A gable end or a triangular plot with a known height | Triangle (base & height) | Not fixed |
| Three measured sides and no height | Triangle (three sides) | Yes |
| A round pool, tank base or patio | Circle | Yes |
| A slice, fan or curved corner | Circle sector | Yes |
| A path around a circular bed | Ring or annulus | Yes |
| An oval table or running track infield | Ellipse | Approximate |
| A plot with two parallel edges of different length | Trapezoid | Add the sides |
| A room with a chimney breast or alcove removed | L-shape | Yes |
Why some shapes have no perimeter
A triangle's base and height fix its area completely, but not its shape. You can slide the apex sideways forever, keeping the same height and the same area while the two slanted sides grow without limit. There is no single perimeter to report, so this calculator says so instead of inventing one. Measure all three sides and switch to the three-sides mode and you get both numbers. The same applies to a trapezoid and a parallelogram, where the optional side fields unlock the perimeter once you supply them.
Square footage, acres and hectares
- 1Square footage of a room
Measure wall to wall in feet and multiply. A 20 × 12 ft room is 240 ft². For flooring, add 5 to 10% for cuts and waste before you order.
- 2An acre is 43,560 ft²
That is a square of about 209 × 209 ft, the "Lot ≈ 1 acre" example above. An acre was originally the area one man with one ox could plough in a day, which is why it is such an odd number.
- 3A hectare is 10,000 m²
A clean 100 × 100 m square, and about 2.471 acres. Most of the world outside the US and UK measures land this way, so both appear in the results.
- 4Break awkward plots into pieces
Any complicated outline can be split into rectangles and triangles. Work out each piece, then add them, or use the L-shape mode if it is a rectangle with one bite taken out.
Area is not volume
Area is flat and measured in square units; volume is three-dimensional and measured in cubic units. If you are buying paint, turf, tiles or carpet you want area. If you are buying soil, water, gravel or concrete you want volume, so use the volume calculator, or the concrete calculator if it is a pour. Working out a missing side of a right-angled triangle first? That is the Pythagorean theorem calculator.
A note on precision
The calculator keeps full precision internally and only rounds for display, so the converted units always agree with each other. Your own tape measure is the weaker link: measure twice, and for anything that gets ordered by the square metre, round your final figure up rather than down.
Frequently Asked Questions
How do I calculate the square footage of a room?
Choose the rectangle shape, set the unit to feet and enter the length and width measured wall to wall. A 20 by 12 foot room is 240 square feet. If the room has an alcove or a chimney breast, use the L-shape mode instead and enter the cutout, or split the room into rectangles and add the results.
How many square feet are in an acre?
An acre is exactly 43,560 square feet, or 4,046.856 square metres, which is roughly a square of 209 by 209 feet. Enter any plot here and the acres and hectares tiles are filled in automatically, so you never have to divide by 43,560 yourself.
What is the formula for the area of a triangle?
If you know the base and the perpendicular height it is half the base times the height. If you have measured all three sides instead, this calculator uses Heron's formula: work out s as half the perimeter, then take the square root of s times (s − a) times (s − b) times (s − c). Both modes are in the shape dropdown.
Why does the triangle mode say the perimeter is not fixed?
Because a base and a height do not describe one triangle. You can slide the top corner sideways as far as you like and the area stays identical while the two slanted sides get longer, so there is no single perimeter to report. Measure the three sides and switch to the three-sides mode and you get both the area and the perimeter.
How do I find the area of a circle?
Multiply pi by the radius squared. The radius is the distance from the centre to the edge, which is half the diameter, so if you measured across the whole circle, halve that figure before entering it. The calculator also gives the circumference, which is what you need for edging or fencing.
Can I mix feet and inches, or metres and centimetres?
Every field uses the single unit you choose, so convert the odd measurement first and use decimals: 7 feet 6 inches is 7.5 feet, and 2 metres 40 centimetres is 2.4 metres. Mixing units in different fields is the most common way to get an area that is wrong by a factor of twelve.
How do I work out the area of an irregular shape?
Split it into simple shapes, calculate each one and add them together. Almost any outline breaks down into rectangles and triangles. If your shape is a rectangle with one corner missing, the L-shape mode does the subtraction for you in a single step.
Is the area calculator free and is my data stored?
It is completely free with no sign-up, and every figure is calculated inside your browser, so nothing you measure is sent to a server or saved anywhere. Once the page has loaded it keeps working without a connection.