At the end of last year start of this year I decided to start using liquid yeasts (culture them up from commercial bottles, actually) and was a bit concerned at how I would know how much yeast to pitch. I discovered that I needed about 150bn cells per brew but I found different/conflicting opions on how to go about measuring that amount of cells.
I then found out that it's actually really hard for HBers to overpitch and it's more of a problem for commercial brewers, so now I just guesstimate how much yeast I need, erring on the side of growing up far more than is needed than too little so I don't underpitch
This obviously doesn't help you, but good luck anyway