⬛Area Calculator

About this calculator

Pick a shape, type its measurements, read area and perimeter with the formula written underneath. It covers the shapes real problems are made of: rectangle, square, circle, triangle by base-and-height, triangle by three sides (Heron's formula — no height needed), trapezoid and ellipse. Impossible triangles are called out rather than silently computed.

Getting real-world areas right

The universal method for rooms, gardens and anything irregular: sketch it, slice it into rectangles and triangles, compute each, add. Nearly every floor plan yields to that decomposition. The details that catch people: a triangle's height is the perpendicular distance to the base, not the slanted side's length (when all you have is the three sides, that's exactly what Heron's formula is for); a circle measured across the middle gives the diameter — halve it before πr²; and units square along with the lengths, so metres in means m² out, and mixing centimetres with metres in one calculation is the classic silent error. Practical margin: for paint, turf or tiles, add 10% to the computed area for cuts and waste. Convert units first, and for volumes rather than areas, multiply by the depth — a 12 m² patio at 0.1 m deep needs 1.2 m³ of concrete.

Frequently asked questions