In truth, there's little reason to need to precisely calculate your blood alcohol volume. The legal limit in the States is so low that an Irishman can get you arrested simply by belching into your face. If you've had more than a single drink in the last few hours, you're likely over the legal limit... and even if you aren't, cops pulling you over have quotas to make.
Still, from a purely scientific perspective, I love the Last Call iPhone app, which allows me to measure my likely drunkenness at any time. You simply plug in what booze you're drinking, when you drank it and how much you weigh and it tells you whether you are above or below the legal limit. Well soused, positively jactitating? It'll let you look up numbers of taxi cab companies or even DUI attorneys.
.016 Brownlee, signing out.