How do you find perimeter with area?

How do you find perimeter with area?
Firstly, what is the shape of the area?
If it is a circle, then using pi x r squared divide the area by 3.142 and take the square root of the answer. Double that and multiply by 3.142 and you have the length of the circle perimeter.
If it's a square (i.e. all sides are equal) take the square root of the area. This gives you the length of one of the sides. Multiply by 4 and you have the perimeter.
For other shapes it gets more difficult. And for some it's nearly impossible. For example you might have an oblong that has an area of 10 square inches. That could be an oblong of 5" x2". It could also be 10,000" x 0.001".
The more closely the area resembles a circle the smaller is the perimeter compared with the area.