Area Calculator

Calculate the area of any common shape

Area is one of the most fundamental measurements in mathematics, engineering, construction, and everyday life. Whether you are calculating how much paint covers a wall, how much flooring you need for a room, how much fabric is in a pattern piece, or solving a geometry problem, area calculation is essential. This calculator handles five common shapes instantly: rectangle, circle, triangle, square, and trapezoid.

Rectangle

A rectangle's area is length multiplied by width: A = l × w. A room 5 metres wide and 4 metres long has an area of 20 square metres. The area of a rectangle is the basis for most building and interior design calculations.

Circle

A circle's area is pi times the radius squared: A = π × r². The radius is half the diameter. A circular garden with a diameter of 6 metres has a radius of 3 metres and an area of π × 9 ≈ 28.27 square metres. For a circle, the area grows quadratically with radius — doubling the radius quadruples the area.

Triangle

A triangle's area is half the base times the perpendicular height: A = ½ × b × h. The height must be the perpendicular distance from the base to the opposite vertex, not the length of a slanted side. A right triangle with legs 3 and 4 has area ½ × 3 × 4 = 6 square units.

Square

A square's area is the side length squared: A = s². This is a special case of the rectangle formula. A 10-centimetre square has an area of 100 cm² = 0.01 m².

Trapezoid

A trapezoid (or trapezium in British English) has two parallel sides called bases. Its area is half the sum of the parallel sides times the perpendicular height between them: A = ½ × (a + b) × h.

Units

The area is always in square units: if dimensions are in metres, area is in m²; in feet, ft². To convert: 1 m² = 10.764 ft². 1 ft² = 0.0929 m².

Practical applications

Flooring: Measure the length and width of a room to find the area. Add 10–15% for waste from cuts.

Paint coverage: Paint covers approximately 10–12 m² per litre (100–130 ft² per quart). Divide the wall area by the coverage rate to find the number of litres needed.

Land and real estate: Land is measured in square metres (most countries) or square feet (US). 1 hectare = 10,000 m². 1 acre = 43,560 ft² ≈ 4,047 m².

Fabric and sewing: Pattern pieces are measured by area to estimate fabric requirements.

Agriculture: Field sizes, crop yield per area, and irrigation planning all use area calculations.

Converting between area units

The same physical area can be expressed in many different units: 1 square metre equals 10,000 square centimetres or 1,000,000 square millimetres; 1 square foot equals 144 square inches; 1 square yard equals 9 square feet; 1 acre equals 43,560 square feet, or about 4,046.86 m²; 1 hectare equals 10,000 m², or about 2.471 acres; 1 square kilometre equals 100 hectares; and 1 square mile equals 640 acres, or about 2.590 km². Keeping a few of these conversions in mind makes it much easier to sanity-check a result that comes out in an unfamiliar unit.

Area of composite shapes

Real rooms and spaces are rarely perfect rectangles. To calculate the area of an irregular space, divide it into simple shapes such as rectangles and triangles, calculate each area separately using this calculator, and add the results together — subtracting any holes or voids such as columns, pillars or other non-floored areas along the way. This divide-and-conquer approach handles almost any real-world floor plan even though the calculator itself only computes one clean shape at a time.

Common area mistakes

The most frequent error is mixing units mid-calculation — measuring one wall in metres and another in feet, then adding the two areas together as if they were the same unit. A second common mistake is using the slant length of a triangle's side instead of its perpendicular height, which always overstates the true area since the slant side is longer than the perpendicular distance whenever the triangle is not a right triangle with that side as the height. A third is forgetting that doubling every dimension of a shape quadruples its area rather than doubling it, since area scales with the square of linear dimensions — a mistake that leads people to badly underestimate how much more paint or flooring a "twice as big" room actually needs.

Estimating area without a tape measure

When an exact measurement is not available, a few rough anchors help sanity-check a guess: a standard door is about 2 square metres, a parking space is roughly 12 to 15 square metres, and a standard sheet of A4 paper is about 0.06 square metres. Comparing an unfamiliar space against a few of these familiar reference areas is often enough to catch a measurement or unit error before it causes a real problem, such as ordering far too little or too much material.

Choosing the right shape

If a space does not match any of the five shapes exactly, pick the closest approximation and accept the small error, or split the space into two or more of these basic shapes and add the results — the composite-shape technique covered above. Either approach beats guessing a single number outright.

Private and instant

All calculations run entirely in your browser, so the result updates instantly as you adjust any dimension and no measurements you enter are ever sent to a server, logged or shared.