1) this IS much more complicated than you thought
2) You are probably asking the wrong question
Here goes: Black & White 35mm Film's resolution has been estimated (high grade) at 7,200,000,000,000 Pixels equivalent BUT then you have to develop it and print it and each step costs resolution (and even paper is graded fine, very fine, extra fine, etc.) (color a bit less at 800,000,000,000 Pixels) (we are not talking about lenses, etc. just the film itself)
NOTE - viewing on screen is even worse - video displays are from 72 DPI (normal) to 96 DPI (very expensive) - nowhere near the 300 dpi of cheap printers
To test this take your old filmstrips and enlarge them onto a ten foot wall. Now try doing the same with digital (ooooops!)
Which is not the point; what people are referring to when they give a figure of 8MP is that to your eye when you make an 8MP print on a 300 dot per inch printer on an 8 x 10 paper you can't tell the difference (some people claim they can tell the quality to 1200 DPI, canon makes printers that print 9600 DPI (at which point your 8 MP image is less than 1/2 inch wide!)
Digital was always meant to be a CONVENIENCE medium - it is so much easier to deal with than film, and that is the selling point; easier to make cameras for, easier to "develop", easier to edit, etc. It was never meant to be the quality medium that film is (look at movies)
So Don't worry about the resolution of film, you will never get there anyways (and neither did prints, remember those paper grades?). 8MP gets you more than a 300 DPI printer will print at 8 x 10, the rest gets wasted and that is all that should be important to you
It's all about the Viewing medium, you are throwing away pixels anyways