Area Calculator

How it works

This calculator covers five plane shapes, each with its own standard geometry formula:

• Rectangle: length × width
• Square: side²
• Circle: π × radius²
• Triangle: base × height / 2
• Trapezoid: (base1 + base2) × height / 2, where base1 and base2 are the two parallel sides

Choose a unit system — metric (dimensions in meters, result in m²) or imperial (dimensions in feet, result in ft²) — before entering your numbers. The result always shows the figure in the unit system you entered, plus a second line with the equivalent in the other system, converted using the exact factor 1 ft² = 0.3048² = 0.09290304 m² (from the international foot definition). That way you get both figures without switching the selector and recalculating.

Every dimension has to be a positive number: zero or negative doesn't describe a real shape, and dimensions above 100,000 (meters or feet) are rejected too, since that's far beyond any realistic room, building, or plot and is far more likely to be a typo — an extra digit, or feet entered where meters were meant — than a real measurement.

The height of a triangle is not a side

The height is the perpendicular distance from the base to the opposite corner, not the length of a slanted side. Take an isosceles triangle with a 10 m base and two slanted sides of 13 m. Half the base is 5 m, so the height is √(13² − 5²) = √144 = 12 m, and the area is 10 × 12 / 2 = 60 m². Multiplying the base by a slanted side would give 65 m², which is too much. The same applies to the trapezoid: use the perpendicular distance between the parallel sides, not the length of a slanted leg.

Radius or diameter

The circle formula uses the radius. Typing a diameter in its place makes the area four times too large, because doubling a length quadruples the area. A round table 3 m across has a radius of 1.5 m and an area of π × 1.5² = π × 2.25 ≈ 7.0686 m², not 28.27 m².

Shapes the tool does not have

L-shaped rooms, rings and other composite shapes are built from the five basic ones. Calculate each piece, then add the pieces or subtract a missing part. Add the unrounded figures if you can, and round only the final answer.

Square meters and square feet

The relationship is 1 m² = 10.7639 ft², more exactly 1 / 0.09290304 = 10.76391 ft². Because it comes from squaring the length factor, never convert an area with the length factor itself: 1 m = 3.28084 ft is for lengths. A 45 m² apartment is 45 × 10.76391 ≈ 484.38 ft², while 45 × 3.28084 = 147.6 would be wrong. In the other direction, 850 ft² is 850 × 0.09290304 = 78.9676 m², shown as 78.97 m².

Decimals and rounding

Numbers are read the way your language writes them, so in English 1,234.56 is one thousand two hundred thirty-four and fifty-six hundredths. Mixed units such as 6 ft 4 in need converting first: 4 / 12 = 0.3333, so enter 6.3333 ft. The area is computed at full precision. Only the display is rounded: the main result shows up to 4 decimals and the other system's figure up to 2. So 2.5 m × 1.333 m = 3.3325 m² appears as 3.3325 m², with 35.87 ft² underneath.

Gross and net area

The same room can have more than one area, depending on where you measure. Gross area usually means measuring to the outside face of the walls, while net or usable area means the floor inside the walls. Property listings, floor plans and contracts may follow different conventions, so check which one a figure refers to before comparing two flats. This tool only multiplies what you enter. For a 10 × 8 m building with 0.3 m thick walls all around, the outer area is 80 m² and the inner floor is (10 − 0.6) × (8 − 0.6) = 9.4 × 7.4 = 69.56 m².

Examples

Rectangle. A room that's 5 m by 3 m has an area of 5 × 3 = 15 m².

Circle. A circular table with a 2 m radius covers π × 2² = π × 4 ≈ 12.57 m².

Triangle. A triangular plot with a 6 m base and a 4 m height has an area of 6 × 4 / 2 = 12 m².

Trapezoid. A trapezoid-shaped garden bed with parallel sides of 3 m and 5 m and a height of 4 m has an area of (3 + 5) × 4 / 2 = 16 m².

Unit conversion. A 10 m × 10 m square is 100 m², which the result also shows as roughly 1,076.39 ft² — useful if you're comparing a metric floor plan against an imperial one. Going the other direction, a 20 ft × 5 ft rectangle is 100 ft², shown alongside its metric equivalent of about 9.29 m².

An L-shaped room. The outer rectangle is 8 × 6 = 48 m² and the missing corner is 3 × 2.5 = 7.5 m², so the room is 48 − 7.5 = 40.5 m². Cut the other way, 8 × 3.5 = 28 m² plus 5 × 2.5 = 12.5 m² is 40.5 m² again, a handy check. In square feet that is 40.5 × 10.76391 ≈ 435.94 ft².

A trapezoid room. A room whose parallel walls are 6 m and 4 m, 5 m apart, has (6 + 4) × 5 / 2 = 25 m².

A ring. A circular flower bed with a 5 m outer radius and a 4 m inner radius: π × 5² − π × 4² = π × (25 − 16) = 9π ≈ 28.2743 m². Run the circle twice, 78.5398 and 50.2655, and subtract.

Things to watch for

• Every dimension must be greater than zero. A side, radius, base, or height of 0 or less doesn't describe a shape, so the calculator shows an error instead of a meaningless or negative area.
• Dimensions above 100,000 (meters or feet) aren't accepted. That limit exists to catch obvious typos — an accidental extra zero, or a unit mix-up — not because a larger real shape couldn't exist.
• Use one unit for all dimensions. Convert centimeters to meters first (320 cm is 3.2 m) before entering them.
• This is general plane geometry, not a legal or survey measurement. For property boundaries, land registry filings, or anything that needs an official measurement, use a licensed surveyor's figures rather than a quick geometric estimate.
• A trapezoid needs the two parallel sides identified correctly. Mixing up which sides are "base1"/"base2" (the parallel ones) and which is the non-parallel side gives a wrong result — only the two parallel sides and the perpendicular height belong in this formula.
• Everything runs in your browser. No dimension you enter is sent to a server; the calculation happens locally on your device.

To turn an area into materials, use the tile calculator or the paint calculator.