One way to do this is to use a step wedge (purchased, or make one yourself) and place it between two sheets of paper, based on the premise that the step wedge will replicate the density of a paper negative. More directly, you could also make yourself a step wedge on paper ie. say 21 steps from 0 to 1 in 5% steps.

Do test strips for time and filtration until the step wedge nicely reverses and each step is discernable, then record aperture, height, time, etc. You are right -- this will need to be found for your paper, your lamp, and your chemistry.