None of mine are the same, good point Steve. What I did was start noting on mine how many 750 ml bottles I got from each when I bottle. That way I can use that to advantage when racking. Most of my 5 gallon (US) are about 25.3 bottles, I have a few 26 and more too.
How do you operate a small winery 311Franco - apologies if my response seems discourteous, it is not meant to be so. But I think that you might start by taking some winemaking clbuttes...
You could reverse your idea and just apply tape to full carboys and as bottled mark them off. I would use medical cloth tape, it will never come off or dry out if you pick the right one.
Charles, I can't think of any chemical addition that has to be that precise anyway. When you add acid, it's always just close to right. The additions are ballpark, the quanbreasty required is not necessarily standardized since your wine is a combination of several acids.
Fining trials are usually set up in half strength increments so there is no need to get precise there either.
Just my two cents. If you have newer carboys my rule of thumb is the quanbreasty to the first blister ring is 1-2 gallon, each ring after that 1 is a gallon and the top ring to the neck holds about 1-2 gallon.
Joe
