Pick a shape, enter its dimensions and get the area instantly — converted to square metres, square feet, acres and hectares — with the formula worked through.
How to use the area calculator
Choose a shape from the menu, select the unit your measurements are in, and enter the dimensions shown. The area appears immediately in that unit squared, together with conversions to square metres and square feet and — for larger areas — hectares and acres. Where a perimeter is defined by the inputs (rectangle, square, circle, ellipse and sector), it is shown as well. Open the table for the same area in every common unit, from square millimetres to square kilometres.
Area formulas for common shapes
| Shape | Formula | What the letters mean |
|---|---|---|
| Rectangle | A = l × w | length, width |
| Square | A = s² | side |
| Triangle | A = ½ × b × h | base, perpendicular height |
| Circle | A = πr² | radius |
| Trapezoid | A = ½ × (a + b) × h | the two parallel sides, height between them |
| Parallelogram | A = b × h | base, perpendicular height |
| Ellipse | A = π × a × b | semi-major and semi-minor axes |
| Sector | A = (θ ÷ 360°) × πr² | central angle in degrees, radius |
Worked examples
Rectangle. A room measuring 8 m by 5 m has an area of 8 × 5 = 40 m², which is about 430.56 ft². Its perimeter — useful for skirting boards — is 2 × (8 + 5) = 26 m.
Triangle. A gable wall with a 10 m base and 6 m peak height has an area of ½ × 10 × 6 = 30 m².
Trapezoid. A garden bed with parallel edges of 6 m and 10 m, 4 m apart, has an area of ½ × (6 + 10) × 4 = 32 m².
Sector. A 60° slice of a circle with a 5 m radius covers 60/360 × π × 25 ≈ 13.09 m² — exactly one-sixth of the full circle.
Measuring irregular areas
Most real spaces are not perfect shapes. The reliable approach is to divide and conquer: split an L-shaped room into two rectangles, a lawn into a rectangle plus a semicircle, or a plot into triangles. Calculate each piece separately and add them up. For cut-outs — a kitchen island, a pond, a chimney breast — subtract their area from the total.
Units and conversions
Area units are squared length units, so conversions are squared too. One metre is 100 centimetres, but one square metre is 100 × 100 = 10,000 square centimetres. One foot is 12 inches, so one square foot is 144 square inches. Mixing units is the most common source of error: if a room is 4 m by 350 cm, convert both to metres (4 × 3.5 = 14 m²) before multiplying.
- 1 m² ≈ 10.764 ft² and 1 ft² ≈ 0.0929 m²
- 1 hectare = 10,000 m² ≈ 2.471 acres
- 1 acre = 43,560 ft² ≈ 4,046.86 m²
- 1 km² = 100 hectares ≈ 247.1 acres
Height must be perpendicular
For triangles, parallelograms and trapezoids, the height is the straight-line distance at right angles to the base — not the length of a slanted side. If you only know the side lengths of a triangle, use the triangle calculator, which applies Heron's formula. For circles defined by diameter or circumference, the circle calculator will find the radius first. For practical home projects measured in feet, the square footage calculator handles multiple rooms at once.
Cite or link to this page
Using this area calculator in an article, report or homework? Copy a citation or a ready-made link:
Calcivia. (2026). Area Calculator. Retrieved October 31, 2026, from https://www.calcivia.com/area-calculator/"Area Calculator." Calcivia, 2026, https://www.calcivia.com/area-calculator/. Accessed 31 Oct. 2026.<a href="https://www.calcivia.com/area-calculator/">Area Calculator</a> by Calcivia