Quick answer: Area is the amount of surface a shape covers: a rectangle is length × width, a triangle is ½ × base × height, and a circle is π × radius². A 12 ft by 10 ft room is 120 square feet, which is 11.15 square meters. For flooring and tiles, add 5 to 15% for waste.
Area tells you how much flooring, paint, turf, carpet or tile to buy, or how big a plot of land is. For a simple room it is length times width, but other shapes such as circles and triangles have their own formulas that are easy to forget.
Pick the shape, choose your unit, enter the measurements, and see the area straight away in square feet, square meters, square yards, square inches, acres and hectares. For flooring and tiles, add a waste allowance to see how much to actually buy.
The formulas
Triangle: ½ × base × height
Circle: π × radius² (circumference 2 × π × radius)
Trapezoid: ½ × (a + b) × height
Ellipse: π × radius A × radius B
To find the area of an L-shaped room or any irregular shape, split it into rectangles, work out each one, and add them up. Make sure every measurement is in the same unit before multiplying: mixing feet and inches is the most common mistake here.
A square foot is a square 1 foot on each side, which is 144 square inches or about 0.0929 square meters. One acre is 43,560 square feet, and one hectare is 10,000 square meters. The ellipse perimeter is an approximation (Ramanujan’s formula), which is very accurate.
A worked example
Example. A rectangular room 12 ft by 10 ft is 120 sq ft, which is 11.15 m² or 13.33 sq yd. A circular patio with a 5 m radius has an area of π × 5² = 78.54 m² and a circumference of 31.42 m. Add 10% for waste when buying flooring or tiles.
Area units
| Unit | In square meters | In square feet |
|---|---|---|
| 1 square foot | 0.0929 | 1 |
| 1 square yard | 0.8361 | 9 |
| 1 square meter | 1 | 10.764 |
| 1 acre | 4,046.86 | 43,560 |
| 1 hectare | 10,000 | 107,639 |
Conversions between common area units.
| Shape | Area formula |
|---|---|
| Rectangle | length × width |
| Triangle | ½ × base × height |
| Circle | π × radius² |
| Trapezoid | ½ × (a + b) × height |
| Ellipse | π × radius A × radius B |
Pick the shape in the calculator and enter the measurements.
Common mistakes to avoid
- Mixing units. Convert everything to one unit before multiplying, because feet times inches gives nonsense.
- Using the diameter as the radius. A circle’s radius is half of its width across.
- Buying exactly the area. Cuts and breakages mean you need extra, more for diagonal patterns or rooms with many corners.
Frequently asked questions
How do I calculate square footage of a room?
Measure the length and width in feet and multiply them. A 12 ft by 10 ft room is 120 square feet. For an L-shaped room, split it into two rectangles and add the areas.
How do I convert square feet to square meters?
Multiply by 0.0929. So 120 sq ft is about 11.15 m². This calculator shows the area in both at once.
How much extra should I buy for waste?
Around 5 to 10% for simple layouts, and 10 to 15% for diagonal patterns or rooms with many corners, to allow for cuts and breakages.
What is the difference between radius and diameter?
The diameter is the full width across a circle, and the radius is half of that. If you measured across, divide by 2 before you enter it.
People also search for this as: square footage calculator, room area calculator, square feet to square meters, area of a circle calculator, how to calculate square footage, flooring calculator.
Sources and further reading
- Area (Wikipedia)
- Square foot (Wikipedia)
- Ellipse, including approximations for the perimeter (Wikipedia)
Formulas on this page are checked by automated tests against independent references. See how we test our tools.