# ISEE Upper Level Math : How to find the diameter of a sphere

## Example Questions

### Example Question #381 : Geometry

There is a perfectly spherical weather balloon with a surface area of  , what is its diameter?

Explanation:

There is a perfectly spherical weather balloon with a surface area of  , what is its diameter?

Begin with the formula for surface area of a sphere:

Now, set it equal to the given surface area and solve for r:

First divide both sides by .

Then square root both sides to get our radius:

Now, because the question is asking for our diameter and not our radius, we need to double our radius to get our answer: