How to Use the Area Calculator

Pick a shape from the list — Rectangle, Square, Triangle, Circle, Trapezoid, Parallelogram, Rhombus, Ellipse, or Regular Polygon — and enter its dimensions. The area updates immediately.

Rectangle:        l × w
Square:           s²
Triangle:         ½ × base × height
Circle:           π × r²
Trapezoid:        ½ × (a + b) × height
Parallelogram:    base × height
Rhombus:          (d1 × d2) ÷ 2
Ellipse:          π × a × b
Regular Polygon:  (n × s²) ÷ (4 × tan(π ÷ n))

Every one of these nine formulas is really the same idea in different clothes — area is always some measure of how much flat space is enclosed, and the differences between shapes are just how conveniently that space can be described with straight measurements versus angles or curves. This page exists as the one-stop version of the site's individual shape calculators, useful when the shape itself is still an open question rather than already decided.