Equable shapes are not regarded as a true mathematical concept, as it is incorrect to state that an area can be equal to a length, however its common use as GCSE coursework has led to it being an accepted term. For any shape, there is a similar equable shape: if a shape S has perimeter p and area A, then scaling S by a factor of p/A leads to an equable shape. Alternatively, one may find equable shapes by setting up and solving an equation in which the area equals the perimeter. In the case of the square, for instance, this equation is
The perimeter of an n-sided regular polygon with side length x is nx. The area is
As with equable shapes in two dimensions, one may find an equable solid, in which the volume is numerically equal to the surface area, by scaling any solid by an appropriate factor.