Area Calculator
Choose a shape, enter its measurements in any one unit, and the area comes out in that unit squared.
Area of a shape
Formulas for each shape
| Shape | Area | Perimeter |
|---|---|---|
| Square (side s) | s² | 4s |
| Rectangle (l × w) | l × w | 2(l + w) |
| Triangle | ½ × b × h | a + b + c |
| Circle (radius r) | πr² | 2πr |
| Ellipse (semi-axes a, b) | πab | ≈ Ramanujan approximation |
| Trapezoid | (a + b) ÷ 2 × h | a + b + c + d |
| Parallelogram | b × h | 2(a + b) |
| Rhombus (diagonals p, q) | pq ÷ 2 | 4s |
| Sector (angle θ°) | (θ ÷ 360) × πr² | 2r + (θ ÷ 360) × 2πr |
| Regular n-gon (side s) | ns² ÷ (4 tan(180°/n)) | n × s |
Worked example
A room 8 m long and 5 m wide
- Rectangle: A = length × width
- 8 × 5 = 40
The floor area is 40 m².
A circle of radius 3 cm
- A = πr² = π × 3²
- = 9π ≈ 28.274
The area is about 28.27 cm².
Units matter
Area is measured in square units. Keep every measurement in the same unit before calculating — mixing 2 m and 50 cm gives nonsense. Remember that area scales with the square of length: 1 m² is 100 × 100 = 10,000 cm², not 100 cm². To switch units afterwards, use the area converter.
Practical tips
- For an L-shaped room, split it into rectangles and add their areas.
- For flooring, paint or turf, add 5–10% for offcuts and waste.
- The “height” of a triangle or parallelogram is the perpendicular height, not the slanted side.