I began seriously tracking several months ago but need to get to the end of a jar for a final answer, with actual pour weight accounted for. My rough estimate right now for Ethos is 3 to 3.5 grams per shave, with a natural hair brush in the 28mm range. I tend to load heavier with natural hair brushes. That usage number generally goes down with a synthetic and or smaller brush. I use those per shave estimates, and measured net weight of a soap, to forecast remaining life of a given jar (as well as my whole collection). Like many here, I am in the multiple year range of remaining soap lifeAnyone ever roughly count how many shaves you get from one 4.5oz Ethos F base tub?
Unfortunately I hand out samples from my personal jars so my numbers would be off.
I just know I use a lot less with my 24mm brushes than I do other soaps (except MdC).