Here's one check: the area of a circle is pi r^2, and each hemisphere of a sphere has area greater than that (since it has the same circular boundary, but is in

Here's one check: the area of a circle is pi r^2, and each hemisphere of a sphere has area greater than that (since it has the same circular boundary, but is inflated), so you know a sphere must have area greater than 2 pi r^2.