Area Calculator
Area and perimeter of rectangles, triangles, circles, ellipses, trapezoids and more, in any unit, with conversions.
Your shape
Filled in with example values. Replace them with your own.
A = length × width
Results update as you type.
Result
Rectangle, length 5 m, width 3 m: area 15 m², perimeter 16 m
Area
15m²
- Perimeter
- 16 m
- mm²
- 15,000,000
- cm²
- 150,000
- m²
- 15
- hectares
- 0.0015
- in²
- 23,250
- ft²
- 161.459
- yd²
- 17.9399
- acres
- 0.00370658
How it’s calculated
Rectangle
length × width = 15 m²
How the area calculator works
Pick a shape, a unit, and enter its measurements. The calculator gives the area in that unit squared, the perimeter where the measurements fix it, and the area in other units from square millimetres to acres.
The formulas
Rectangle: length × width
Triangle: ½ × base × height, or Heron’s formula from three sides
Circle: π × radius²
Ellipse: π × a × b
Trapezoid: ½ × (a + b) × height
Parallelogram: base × height
Sector: angle ÷ 360 × π × radius²
Worked examples
- A 5 × 3 m rectangle: 15 m² (161.46 ft²), perimeter 16 m.
- A triangle with sides 3, 4 and 5: s = 6, √(6 × 3 × 2 × 1) = 6.
- A circle of radius 2 m: π × 4 ≈ 12.57 m².
- A quarter circle (90°) of radius 10 cm: ¼ × π × 100 ≈ 78.54 cm².
Frequently asked questions
How do I find the area of an irregular shape?
Split it into simple shapes, such as rectangles and triangles, work out each area and add them up. For a room with an alcove, for example, measure the main rectangle and the alcove separately.
What if I only know the diameter of a circle?
The radius is half the diameter. A circle 10 cm across has a radius of 5 cm and an area of π × 5² ≈ 78.54 cm².
Why is the ellipse perimeter approximate?
There is no simple exact formula for the perimeter of an ellipse. The calculator uses Ramanujan’s approximation, which is very accurate for everyday shapes and exact for a circle.
How do square units convert?
Square both sides of the length conversion: 1 ft = 0.3048 m, so 1 ft² = 0.3048² = 0.09290304 m². A hectare is 10,000 m² and an acre is 43,560 ft² (about 4,046.86 m²).