To find the surface area of a sphere, you can use the formula:
\[ A = 4\pi r^2 \]
where \(A\) is the surface area and \(r\) is the radius of the sphere.
First, you need to calculate the radius from the given diameter. The radius is half of the diameter:
\[ r = \frac{\text{diameter}}{2} = \frac{40 \text{ inches}}{2} = 20 \text{ inches} \]
Now, substitute the radius into the surface area formula:
\[ A = 4\pi (20)^2 \]
Calculate \(20^2\):
\[ 20^2 = 400 \]
Now substitute this value back into the formula:
\[ A = 4\pi (400) \] \[ A = 1600\pi \]
Thus, the surface area of the sphere is
\[ \boxed{1600\pi} \text{ square inches.} \]