About the Area Calculator
Calculates the area of 10 common 2D shapes, with the formula shown for each.
Supported shapes
Triangle
Base & height, or Heron's formula from 3 sides.
Rectangle & square
l×w or s².
Circle & sector
πr², shown in exact π-form.
Trapezoid & parallelogram
½(b₁+b₂)h and base×height.
Rhombus
½ times the two diagonals.
Regular polygon & ellipse
Trigonometric polygon formula; πab for ellipse.
Validation
Every shape checks for positive dimensions; the 3-side triangle mode additionally checks the triangle inequality before computing an area.