Perimeter of a Rectangle with Given Area Calculator
Our perimeter of a rectangle with a given area calculator lets you find the perimeter of a rectangle once you know the area and a side (length or width).
The formula
A = w × h, P = 2(w + h), d = √(w² + h²)
Area scales with the square
Double every length in a flat shape and the area quadruples; triple them and it grows ninefold. Perimeter, being a length, scales in step with the sides. That mismatch is why bigger shapes enclose proportionally more area per unit of edge — and why a circle, having no corners at all, encloses the most area for a given perimeter of any shape.
Units
Whatever unit you enter, the area comes out in that unit squared and the perimeter in the unit itself. The calculator is unit-agnostic — enter centimetres and read cm and cm², or feet and read ft and ft². Just do not mix units between fields.