Finding the maximum storage of a CD from measurements of pits and lands?
Is looking up the manufacturer's specification of the CD an option?  At the very least knowing the specification could let you verify what you are finding by counting the pits and lands.  

In general I would think that the spacing between each spiral pattern on the disk would be a standard, (equal to the resolution of the reader optics), so the total length of a full track rather then the disk's area should be the limiting factor.