Area Calculator
Calculate the area of square, rectangle, triangle (base-height or Heron), circle, trapezoid, parallelogram and ellipse with step-by-step formulas.
Start with one measurement unit
Area calculation tells you how much two-dimensional space lies inside a boundary. Before selecting a shape, convert every length to the same unit. Metres produce square metres, centimetres produce square centimetres, and mixing the two without conversion can change the answer by a factor of 10,000.
| Shape | Area calculation formula | Example |
|---|---|---|
| Square | A = a² | a = 6 gives 36 units² |
| Rectangle | A = a × b | 5 × 4 = 20 units² |
| Triangle | A = base × height / 2 | 8 × 5 / 2 = 20 units² |
| Circle | A = π × r² | r = 5 gives about 78.54 units² |
| Trapezoid | A = (a + b) × h / 2 | (4 + 8) × 5 / 2 = 30 units² |
| Parallelogram | A = base × height | 10 × 6 = 60 units² |
| Ellipse | A = π × a × b | 6 × 4 × π ≈ 75.40 units² |
A rectangle needs length and width. A square area calculator uses one side twice because all four sides are equal. For a 5 by 4 rectangle the result is 20 units²; for a square with side 5 it is 25 units². Those formulas assume right angles, so they should not be used for a visibly slanted outline.
A triangle needs a base and the height perpendicular to it. A sloping side is not that height. If the height cannot be measured but all three sides are known, the Heron mode first finds the semiperimeter s = (a + b + c) / 2 and then evaluates A = √(s(s-a)(s-b)(s-c)). The sides must still satisfy the triangle inequality.
Four sides do not fix a unique area
A quadrilateral area calculator cannot normally work from four side lengths alone. Different angles can produce different enclosed areas with the same sides. Trapezoid mode therefore asks for two parallel bases and their perpendicular separation; rectangle and parallelogram modes make their own geometric assumptions. An irregular quadrilateral may require a diagonal, angle, height or vertex coordinates.
Radius, square metres and irregular floors
A circle uses A = πr². Radius r runs from the centre to the edge; if you have the full diameter, halve it first. “Area of a circle calculator” describes the filled region, while circumference refers only to the boundary. The semicircle mode divides the full circle result by two.
An area in square meters calculator expects the underlying lengths in metres. A 250 cm side is 2.5 m, so a 2.5 m by 4 m floor covers 10 m². One square metre equals 10,000 cm². A surface area calculator answers a different question by adding the exposed faces of a three-dimensional solid; this page handles flat shapes only.
For an L-shaped room, split the plan into non-overlapping rectangles or triangles. Add the occupied pieces and subtract recesses. This is often clearer than forcing the outline into one formula, and the calculation line beneath the result lets you check which measurements were actually used.
Frequently Asked Questions About the Area Calculator
The rectangle area calculator multiplies length by width after both are put in the same unit: A = a × b. A rectangle measuring 5 m by 3 m covers 15 m².
The triangle area calculator multiplies one base by its perpendicular height and divides by two. When the three sides are known instead, use Heron's formula after checking the triangle inequality.
The circle area calculator uses A = πr², where r is the radius. Divide a supplied diameter by two first; a circle with a 10 cm diameter has an area of about 78.54 cm².
The trapezoid area calculator adds the parallel sides, multiplies by their perpendicular separation and divides by two: A = (a + b) × h / 2. A sloping leg cannot replace h.
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