Area calculator
Compute the area of a rectangle, circle, triangle, ellipse or trapezoid; a 4 × 3 m rectangle is 12 m².
- Runs in your browser
- No upload
- Instant result
Assumptions & formula
Formula and assumptions
AB; πA²; AB/2; πAB; (A+B)H/2
Results
Enter values and press Calculate to see the result here.
How to use this calculator
- Set inputs and units
Choose a shape and put every measurement in the same unit. Rectangle: length and width; circle: radius; triangle: base and perpendicular height; ellipse: two semiaxes; trapezoid: two parallel sides and perpendicular height. A square uses rectangle mode with equal length and width. Match the letters to the shape diagram.
- Calculate
Check this worked example: rectangle: a=4 ft,b=3 ft → area=12 ft²; circle: radius=2 m → 4π m²
- Results
Read the area in the square of your input unit: feet give ft² and meters give m². The unit selector labels your measurements; changing it does not convert the numbers already entered. Convert all lengths before calculating. For example, 4 ft × 3 ft is 12 ft², not 12 m².
Questions and limits
Does the circle field take diameter?
It takes the radius. For an ellipse, a and b are semiaxes, so halve measured diameters first.
Which input errors should I correct?
Use positive dimensions in one unit. A triangle’s height must be perpendicular, and a trapezoid’s height is not a sloping side.
What does this calculation leave out?
Calculate one ideal shape at a time. For an L-shaped floor, split it into non-overlapping rectangles, calculate each in the same unit and add the areas. Calculate openings separately and subtract them. There is no map tracing, automatic irregular-polygon calculation, perimeter output or allowance for measurement tolerances.