Tumbler capacity (in pounds or quarts) dictates the amount of media. The goal is to add enough media to get the cases to either not be visible or just occasionally be visible as the tumbler runs (during the time the case sticks up in the air it is not being cleaned).

The amount of polish used changes. Initially it takes a fairly large amount - again dependent on the size of the tumbler. Subsequent batches run through the tumbler take significantly less.

We have two tumblers, a huge Frankford (capacity about 1200-1300 9mm cases) that takes most of a fluid ounce to 'charge' the media initially. But subsequent batches of brass, I seldom add more than perhaps a teaspoon full at most. Also a Lyman 750 tumbler - about 1/2 the capacity. Probably won't surprise you to hear I use about half as much polish in that one.

It is important to note; DO NOT add polish with cases already in the tumbler. Add the polish, run the tumbler until you see NO MORE 'lumps', then add the cases. Otherwise you will find one of those Murphys laws; polish wet media lodges inside the cases and gets really really sticky and difficult to clean out.