There is no accurate way to determine what you want to know without densitometric readings. Each film/developer combination will respond differently. Complicating this still further would be your agitation procedure and your water temperatures. The next thing that enters into this is the ES of the paper that you are using.
While a densitometer works fine and can save you some testing time, it's not at all necessary.
For all Fred Picker's bombast, he did outline a simple and reliable method of testing for both film speed and development times. (This is a modification.)
Buy a small (1 1/2 inch square) .10 Wratten neutral density gelatin filter. Gelatins are delicate so handle it with care.
Expose several sheets of film of a blank, non-testured surface in open shade in half-stop increments for a Zone I density. (4 stops down from your meter reading; meter should be set at recommended speed for the film).
Develop at recommended development time for that film.
Over a light box, place the Wratten .10 filter over a piece of the clear film leader and take a reading with your spot meter held flat against the film/filter sandwich. Use the EV numbers on your meter.
Let's say your EV reading is, for example, 9.6. This is your FBF (film-base-plus-fog) number and will remain constant for that particular film.
Now, lay each of your test negs on the lightbox (without the filter) and read each of them in turn. The one that is equivalent to your FBF reading is your Zone I and this gives you the speed of your film.
Now shoot about 4-5 more sheets of film, using your tested film speed (same setup), but this time at 3 stops over the meter reading for Zone VIII.
Develop the first sheet at recommended time.
Find the enlarger exposure that gives you the minimum time to get a maximum black. (Clear film in the neg. carrier--test strip in 3-second increments. The strip that is the first one to be indistinguishable from the one following it is the correct time.) Let's say, for example, 9 seconds at f/11.
Now put your test neg in the neg carrier and expose a test strip for your MTMB exposure of (e.g.) 9 secs., covering half of the test strip during the exposure.
If you cannot see a difference between the uncovered and covered portion of the test strip, (pure white), your development time is too short. Develop another of your test negs at 20% more time, and do another test print. You're looking for a very light gray, just distinguishable from the pure white of the covered part of the strip. If it's darker than that, you've overdeveloped, and your Normal development time is probably somewhere between the recommended time and your 20% increment. At any rate, splitting the difference will be "close enough for government work" as Pat Gainer is fond of saying.
With normal time established for that film at that speed, use your remaining test negs to establish an N+ and an N- time. N+1 is approximately one stop difference in density, etc.
I rarely use more than an N+1 and almost never more than an N-1. Depends on the film, and T-grain films like T-Max or Delta don't seem to need as much over and under development as older-type more conventional films.
This sounds complicated, but in practice, it's easy enough, if a bit time-consuming and tedious. But once you've done the testing, you won't have to re-do it until you decide to change films. And even then, you can cheat and make a guesstimate based on your previous results. Most times, you'll get fairly close on the first guess, and can fine tune it by eyeball rather than repeating the whole procedure again. It's worked for me.
