Geometry calculator
Pick a shape and type its measurements.
Deliberately unitless: the answers come out in whatever unit you type in. Centimeters in means square centimeters out. Mixing units within one shape is the one mistake this page could cause, so it does not offer a unit picker - the unit converter is a click away.
What the answers mean
Everything here is unitless on purpose. Put centimeters in and the area is in square centimeters and the volume in cubic centimeters; put inches in and you get square and cubic inches.
That is why there is no unit selector. A selector invites the one error this page could actually cause - a width in centimeters beside a height in inches - and produces a number that is confidently wrong. Convert first, then measure.
Two results that are approximations, and say so
An ellipse's perimeter has no exact formula. The figure here uses Ramanujan's second approximation, accurate to better than one part in a billion for any ellipse you are likely to type, and it is labelled as an approximation rather than passed off as exact.
A triangle from three sides uses Heron's formula, and the calculator checks the triangle inequality first - each side has to be shorter than the other two added together. Three lengths that cannot close into a triangle produce a message saying so, rather than a blank box that reads as a bug.