Area in one step
Area is the amount of flat surface inside a shape. You need it to buy flooring, turf, paint, tiles or fabric, to compare rooms and plots, or to finish a geometry exercise. This area calculator covers the five shapes people ask about most: rectangles and squares, triangles, circles, trapezoids and ellipses.
Measure the sides in any unit. The answer comes back in square units of that same measure, so feet give square feet and metres give square metres, and it is also converted into square metres, square feet, square yards, acres and hectares.
How to use it
- Choose the shape. A square is a rectangle with equal sides.
- Type the measurements. For a triangle, the height goes straight up from the base at a right angle, not along a sloping side.
- Pick the unit you measured in.
- Read the area, then the same area in the other square units below it.
For an L shaped room or an odd plot, split it into rectangles and triangles, find each area, and add them. The square footage calculator can add several parts for you.
Area formulas
rectangle: area = length × width
triangle: area = base × height ÷ 2
circle: area = π × radius²
trapezoid: area = (a + b) ÷ 2 × height
ellipse: area = π × a × bEvery formula multiplies two lengths, which is why area is always in square units. A triangle is half of a rectangle with the same base and height. A trapezoid uses the average of its two parallel sides. An ellipse is a stretched circle, so its two half widths take the place of the radius squared.
Worked example: a 12 by 15 foot room
- Area: 12 ft × 15 ft = 180 ft²
- In square metres: 180 × 0.3048² = 180 × 0.09290304 = 16.7225 m²
- In square yards: 180 ÷ 9 = 20 yd²
The room is 180 ft², or 16.7225 m², or 20 yd². Flooring is usually sold by the square foot or square metre, and carpet sometimes by the square yard, so all three are worth having. Add about 5 to 10% when you order, for cuts and offcuts.
Square unit conversions
| Unit | Equals |
|---|---|
| 1 square foot | 144 in², or 0.09290304 m² |
| 1 square yard | 9 ft², or 0.83612736 m² |
| 1 square metre | 10.7639104 ft² |
| 1 acre | 43,560 ft², or 4,840 yd², or 4,046.8564224 m² |
| 1 hectare | 10,000 m², or 2.4710538 acres |
These come from exact length definitions: 1 foot is 0.3048 m, so 1 ft² is 0.3048 × 0.3048 m². Converting area is not the same as converting length. A metre is about 3.28 feet, but a square metre is about 10.76 square feet. For lengths alone, use the unit converter.
Common slips
- Mixing units, such as feet for the length and inches for the width. Convert first, or measure both sides the same way.
- Using the slanted side of a triangle as its height.
- Using the diameter in the circle formula. The radius is half of it.
- Converting square units with a length factor. Square the factor: 1 yd² is 9 ft², not 3.
Frequently asked questions
How do I calculate area?
It depends on the shape. For a rectangle, multiply length by width. For a triangle, multiply base by height and halve it. For a circle, multiply π by the radius squared. Choose the shape above, type the measurements, and the calculator does the rest, in any unit you measured in.
How do I find the area of an irregular shape?
Split it into simple shapes, such as rectangles and triangles, that do not overlap. Find the area of each part and add them together. For a cut out section, such as a chimney breast in a room, find its area and take it away from the total.
How many square feet are in a square metre?
One square metre is 10.7639104 square feet. That comes from squaring the exact length factor: 1 metre is 3.2808399 feet, and 3.2808399 squared is about 10.764. Going the other way, one square foot is exactly 0.09290304 square metres, so a 200 square foot room is about 18.58 square metres.
What is the difference between area and perimeter?
Area is the surface inside a shape, measured in square units. Perimeter is the distance around the edge, measured in plain units. A 12 by 15 foot room has an area of 180 square feet but a perimeter of 54 feet. Skirting boards follow the perimeter, while flooring covers the area.
How many square feet is an acre?
An acre is exactly 43,560 square feet, which is 4,840 square yards or about 4,046.86 square metres. A square acre would measure about 208.7 feet on each side. A hectare is larger: 10,000 square metres, or about 2.47 acres, which is the unit most countries use for farms and land.
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