Im no expert, but as far as im aware, different people could give different reading's after drinking the same amount. All depends on weight, height, what you've eaten and how often you drink etc. But at a very rough guess I would say 50 on a breath test would be about two and a half to 3 pints of medium lager? Which is what about 6 units? Like I say im no expert, I am attending my rehab course in november, and from what I've read on this site, you really get to learn about units and how long it takes to come out of your system etc.