text: how does one find the volume of just part of a sphere? i have a problem that wishes for me to find the volume of only part of the sphere. r=4.5m and the question wishes the sphere to be filled to 6.5m. i know i should know this...(ap trig) thanks a million for any help. a formula would be great! compute for the total volume of the sphere and subtract the empty portion of the sphere.  the volume of the sphere is:  v = 4/3 pi r^3  the volume of the empty portion (spherical cap):  v = 1/3 pi h^2 (3r - h)  h is the height of the empty portion.