How to Find Area – Formulas for Common 2D Shapes

First identify the shape and the measurements you know. Then select the area formula that matches that shape, substitute the measurements, calculate, and report the result in square units. For example, a rectangle uses A = L × W, while a triangle uses A = ½bh and a circle uses A = πr². If the figure is irregular, split it into simple shapes and add or subtract their areas.

A useful check is to compare your result with a simple bounding rectangle. If a shape fits inside a 10 m × 6 m rectangle, its area cannot exceed 60 m² unless your interpretation of the dimensions is wrong.

Area measures two-dimensional surface, so it combines one length direction with another. A rectangle 4 m long and 3 m wide contains 4 × 3 = 12 squares that are each 1 m by 1 m. Each unit square has an area of 1 m², which is why the result is 12 m².

This is also why converting area units requires squaring the length conversion. A foot is 0.3048 m, but a square foot is 0.3048² = 0.09290304 m².

Area measures the surface inside a closed shape, while perimeter measures the total distance around its boundary. They therefore use different units. Area is measured in square units such as m² or ft²; perimeter is measured in ordinary length units such as m or ft.

For a 6 m × 4 m rectangle, area = 6 × 4 = 24 m². Perimeter = 2(6 + 4) = 20 m. The same object can therefore have both an area and a perimeter, but the numbers describe different physical quantities.

If the shape is a rectangle, multiply the length by the width: A = L × W. Both measurements must refer to perpendicular directions and should use the same unit. For a 12 ft × 9 ft room, A = 12 × 9 = 108 ft².

If the shape is not rectangular, length × width may only give the area of a bounding rectangle, not the actual figure. In that case, use the formula for the actual shape or divide the figure into components.

Break the irregular figure into shapes with known formulas—commonly rectangles, triangles, circles or semicircles. Calculate each part, then add regions that belong to the figure and subtract holes or cutouts. For an L-shaped room, for example, you can split the floor into two rectangles and add their areas.

The important rule is to create a decomposition that does not double-count overlapping regions. For more complicated layouts, split the space into simple shapes, find each area with the Area Calculator, and add them.

Yes, when the shape and enough other information are known. Rearrange the area formula to isolate the missing measurement. For a rectangle, A = LW becomes L = A/W or W = A/L. For a triangle, A = ½bh becomes h = 2A/b when the base is known. For a square, A = s² becomes s = √A.

This is an algebra problem using the same geometric relationship in reverse. The Area Calculator includes several reverse-solving modes.

For a rectangular area measured in feet, multiply length in feet by width in feet. A 14 ft × 11 ft room has 154 ft². If measurements include inches, either convert the inches to decimal feet first or convert everything to inches and divide the final square-inch result by 144.

For L-shaped or multi-room spaces, calculate each rectangle separately and add the areas. See the dedicated How to Calculate Square Footage guide for rooms, walls and irregular layouts.

The calculator can produce many decimal places, but real accuracy depends on the measurements. If a wall was measured only to the nearest centimetre, reporting area to six decimal places implies more precision than the input supports. Keep enough digits for the purpose, and round only after the main calculation rather than repeatedly during intermediate steps.

For purchasing material, the geometric area may also need a separate project allowance for cuts, waste, pattern matching or installation requirements. That allowance is not part of the area formula itself.