What is the diameter of a sphere with a surface area of 1256

The surface area is 1256 square units, which in turn is equal to 4*pi*r^2.

First, solve this for r^2:

1256 square units

r^2 = = 99.95 sq units

4*pi

Then r = 10.00 units, and so the diameter is twice that, or d = 20.00 units.