Area Calculator
Calculate the area and perimeter of squares, rectangles, circles, triangles, and more.
📐 Area Calculator
How to Use
- Choose a shape from the tabs at the top.
- Pick your unit of measurement (applies to every shape).
- Enter the required dimensions for that shape.
- Area (and perimeter, where available) update instantly as you type.
Frequently Asked Questions
QHow do I calculate the area of a triangle if I only know the three sides?
Switch the Triangle tab to "Three Sides" — the tool uses Heron's formula: Area = √(s(s−a)(s−b)(s−c)), where s is the semi-perimeter (a+b+c)/2.
QWhy doesn't the Triangle (Base & Height) mode show a perimeter?
Base and height alone aren't enough to determine the length of all three sides, so no perimeter can be calculated in that mode. Switch to "Three Sides" if you need the perimeter too.
QIs the ellipse perimeter exact?
No exact elementary formula exists for an ellipse's perimeter — this tool uses Ramanujan's well-known approximation, which is accurate to within a tiny fraction of a percent for virtually all practical ellipses.
QCan I convert my result to a different unit afterwards?
Yes — use the site's separate Area unit converter to convert your result (e.g. m² to ft² or acres) after calculating it here.
QIs my data sent to a server?
No. All calculations happen locally in your browser using JavaScript. Nothing is sent to or stored on any server.
About This Calculator
Each shape uses its standard geometric formula: square/rectangle multiply their sides; circle uses πr²; triangle uses ½×base×height or Heron's formula from three sides (with a triangle-inequality check to catch impossible side combinations); trapezoid and parallelogram use their standard base×height-derived formulas; ellipse area uses πab with Ramanujan's perimeter approximation; and regular polygon area uses (n×s²)/(4×tan(π/n)) for n sides of length s. All calculations run client-side in JavaScript.