The short answer, unfortunately, is that you can't.
First, these are not "spheres" at all, but completely irregular, lop-sided shapes. The shape is based on a number of factors:
1.) Signal propagation based on the design of the antenna (which has a shape under ideal conditions, e.g. a vacuum). For instance, an omnidirectional antenna propagates 360 degrees on the horizontal axis.
2.) Sources of interference which may impede or destroy RF signal. (A list of possible sources would best be the subject of another post.)
3.) Barriers for the RF, which either block or attenuate the signal. These may take the form of thick, steel-reinforced walls, stairwells and elevator shafts, etc. A site survey would show the RF shadow caused by such a barrier.
In other words, the propagation of RF is dependent on so many factors, that even if there were a way to give an estimate of distance based solely on the hardware used, it wouldn't be of any real value in practice.
My suggestion would be to have a full professional site survey done to determine the best placement and density of AP's for your environment. If that's not an option for you, do a small pilot (3 AP's or so) and place them in temporary locations in your environment. You can then do a little "trial-and-error" on them to see a) the best locations for installing them permanently, and b) an idea of how many you'd need for the entire site.
Hope this helps! Let us know how you made out.