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About this tool
Calculate the area of 12 shapes — rectangle, triangle, circle, trapezoid, polygon and more — with a labelled diagram, steps and m², ft², acre or hectare units.
This Area Calculator covers twelve shapes: square, rectangle, triangle from base and height, triangle from three sides (Heron's formula), circle, sector, ellipse, trapezoid, parallelogram, rhombus, regular polygon with any number of sides, and annulus. Choose a shape, type its dimensions in any length unit, and the area is calculated with the standard formula, shown step by step with your numbers substituted. The result is converted to the area unit you pick and listed in ten units at once, from mm² to acres and hectares. Perimeter, diagonals, angles or apothem are shown when they apply. You can add or subtract shapes in a running total for L-shaped rooms or plots. Nothing leaves your browser.
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Under Shape, pick one of the 12 shapes such as Rectangle, Triangle 3 sides, Sector or Regular polygon.
Type each dimension (for example Length l = 8 and Width w = 5), then choose the Length unit and an Area unit such as ft², acres or hectares.
Read the area, perimeter and extras in the Area card, check the labelled Diagram and the Steps, and see Area in other units for all 10 units.
For a composite floor plan, press Add to total for each part, tick Subtract for holes, and read the Total area.
From squares and circles to sectors, ellipses, annuli and regular polygons with any number of sides, each with its own inputs and formula.
Enter lengths in mm, cm, m, km, in, ft, yd or mi and read the area in any of ten units, including acres and hectares, with the conversion step shown.
Each result shows the formula, the substituted working and a labelled diagram drawn to your proportions, so you can check the method.
Add several shapes, or subtract holes, to get the area of composite floor plans and land plots, kept in your browser for next time.
| Shape | Area formula | Variables |
|---|---|---|
| Square | A = a² | a = side |
| Rectangle | A = l × w | l = length, w = width |
| Triangle | A = ½ × b × h | b = base, h = perpendicular height |
| Triangle (Heron) | A = √(s(s−a)(s−b)(s−c)) | s = (a + b + c) / 2 |
| Circle | A = πr² | r = radius |
| Sector | A = (θ / 360°) × πr² | θ = central angle in degrees |
| Ellipse | A = πab | a, b = semi-axes |
| Trapezoid | A = ((a + b) / 2) × h | a, b = parallel sides, h = height |
| Parallelogram | A = b × h | b = base, h = height |
| Rhombus | A = (d₁ × d₂) / 2 | d₁, d₂ = diagonals |
| Regular polygon | A = n s² / (4 tan(180°/n)) | n = sides, s = side length |
| Annulus | A = π(R² − r²) | R = outer, r = inner radius |
1 acre = 43,560 ft² ≈ 4,046.86 m²; 1 hectare = 10,000 m²; 1 m² ≈ 10.7639 ft².
Area is the amount of flat surface a shape covers, measured in square units. Each shape has its own formula: a rectangle is length × width, a triangle is ½ × base × height, and a circle is π × radius². Measure the dimensions in the same unit, apply the formula, and the result is in that unit squared.
Measure the length and width of the room in feet and multiply them. A room 12 ft by 15 ft is 180 square feet. For an L-shaped room, split it into two rectangles, find each area and add them. If you measured in inches, divide the square inches by 144 to get square feet.
Use Heron's formula. First find the semi-perimeter s = (a + b + c) / 2, then area = √(s(s − a)(s − b)(s − c)). For sides 3, 4 and 5, s = 6 and the area is √(6 × 3 × 2 × 1) = √36 = 6. The three sides must satisfy the triangle inequality.
Average the two parallel sides and multiply by the height: A = ((a + b) / 2) × h. A trapezoid with parallel sides 4 and 8 and a height of 5 has an area of 6 × 5 = 30 square units. The height is the perpendicular distance between the parallel sides, not the slanted side.
For n equal sides of length s, area = n × s² / (4 × tan(180° / n)). Equivalently, it is half the perimeter times the apothem, the distance from the centre to the middle of a side. A regular hexagon with sides of 2 has an area of about 10.392 square units.
One acre is exactly 43,560 square feet, which is about 4,046.86 square metres or 0.4047 hectares. A square acre measures roughly 208.7 feet on each side. One square mile contains 640 acres. To turn a plot measured in feet into acres, multiply length by width and divide by 43,560.
A hectare is a metric unit equal to 10,000 m², the area of a square 100 metres on each side. An acre is an imperial unit of 4,046.86 m². So one hectare is about 2.471 acres, and one acre is about 0.405 hectares.
Multiply square metres by about 10.7639 to get square feet, or divide square feet by 10.7639 to get square metres. This factor is the square of 3.28084, the number of feet in a metre. Area conversion factors are always the square of the length factor.
A circle's area is πr², so a radius of 5 gives about 78.54 square units. A ring, or annulus, is the area between two circles: π(R² − r²). A washer with an outer radius of 6 and an inner radius of 4 has an area of 20π, about 62.83 square units.
A sector is a slice of a circle between two radii. Its area is the angle as a fraction of 360° times the circle's area: A = (θ / 360°) × πr². A 60° sector of a circle with radius 5 has an area of about 13.09 square units.
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