About the Area Calculator
Work out the area of a square, rectangle, triangle, circle, ellipse, trapezoid, parallelogram, circle sector or any regular polygon, in the unit you measured in, and see the same area in square metres, square feet, acres, hectares and more.
Type the measurements and the answer updates as you go, with the formula and the working shown underneath.
How it works
Each shape uses its standard formula, worked out to 40 significant digits so rounding only happens in what you see. A triangle can be entered by base and height, or by its three sides (Heron's formula), and the tool tells you if three sides can't make a triangle.
Conversions use the exact definitions: 1 inch is 2.54 cm, so 1 square foot is 0.09290304 m², an acre is 4,046.8564224 m² and a hectare is 10,000 m².
Rectangle A = length × width Triangle A = ½ × base × height Circle A = π × r² Trapezoid A = ½ × (a + b) × h Heron A = √(s(s−a)(s−b)(s−c)), s = (a+b+c)/2
Assumptions and limits
- All lengths are in the same unit; the area is shown in that unit squared and converted to the others.
- A regular polygon has equal sides and angles. For an irregular shape, split it into rectangles and triangles and add the areas.
- Use a dot for decimals (12.5), not a comma.
Worked examples
Paint for a wall
A wall 4.2 m long and 2.6 m high is a rectangle of 10.92 m². Take away 1.89 m² for a door (0.9 m × 2.1 m) to get 9.03 m² to paint.
A round table
A table 120 cm across has a radius of 60 cm: π × 60² = 11,309.73 cm², or 1.13 m².
A plot of land
A rectangle 66 ft by 660 ft is 43,560 ft², exactly one acre.
How to use the Area Calculator
- Choose the shape. Square, rectangle, triangle, circle and more.
- Enter the measurements. In mm, cm, m, km, inches, feet, yards or miles.
- Read the area. With the formula, the working and other units.
Frequently asked questions
How do I find the area of an L-shaped room?
Split it into two rectangles, work out each area with this tool, and add them together. Any shape with straight sides can be split into rectangles and triangles the same way.
Do I enter the radius or the diameter of a circle?
The radius, which is half the diameter. If you measured straight across the circle, divide that number by two before entering it, then the area comes out right.
How many square feet are in a square metre?
One square metre is about 10.7639 square feet, because a foot is exactly 0.3048 m and 1 ÷ 0.3048² = 10.76391. Enter your size in metres to see square feet directly.
How accurate are the results?
The formulas are worked out to 40 significant digits with exact unit definitions, so the only rounding is the number of decimal places you choose to display, which you can change.
What if my triangle's sides don't work?
Any two sides of a triangle must together be longer than the third. If they aren't, no triangle has those sides, and the tool says so instead of showing a wrong area.
This tool runs entirely in your browser. What you enter or upload stays on your device and is never sent to our servers.