You can't use dry weight to compare wet weight. Cells are >70% water so you are not starting with the proper weight. I am not sure your goals but the proliferation index equation is C(final)=C(intial)x2^(tf). Where C is your cell count, t is time and f is cell cycle frequency. I would recommend you use absorbance to determine your cell growth curves with a known dilution curve to determine the number of cells. Otherwise look into life technologies website for cell counting kits.