There are a number of possible measurements.(posted 8945 days ago)One is grain size. I wrote up an experiment on Delta 3200 in photo.net, but I can't find the post, and don't seem to have kept a copy.
Another is how much detail can be digitally scrapped from the negative. A figure of 4000 dpi is often quoted, and this is 157 dots per mm. For a 24x36mm negative, this is 21 million dots.
Another is how much detail is recorded by the lens/film combination. This could be 50 lp/mm (line PAIRS per mm), or 100 dots per mm. For a 24x36mm neg, this is 8 million dots.