DUI is .08. But it's not percent even though some signs say that. Breath alcohol is measured in grams per decalitre or .08 grams in a decalitre of breath.
The measurements are close though, or so I'm told. FYI, .3 would be dead or comatose for most people, so IF this guy stumbled in and said anything understandable, he's a hard core conditioned drunk. The amount of beer one would half to brew in their gut to get to that level wouldn't fit. If he weight 100 lbs he'd need 120 ounces of 4.5% in an hour to get there.