Are you referring at least in part to the presumed density of a yeast cake, from a starter, after crashing, McMullan? I seem to recall reading somewhere parsing out your yeast amount from measuring the volume of the cake (or perhaps as a proportion of the spent starter wort on top of it), with a density as an estimate and going from there.No, you can’t. Unless you’re very skilled in the art of counting cells with a microscope and following watertight procedures to collect representative samples, forget all about ‘cell number’. Mass or volume are much better surrogates and more doable for most home brewers. Just be consistent and determine empirically what works best for you. Note too that a 2L starter doesn’t automatically give you (by virtue of volume) 300 billions cells. Seeding an appropriate volume of starter wort with about 75 billion cells does.