Went to school in a college town in the US. I always based it on how much alcohol your body should can process, roughly a beer an hour. So if I started drinking at a party four hours ago and had five beers, I figured I was sober enough to go home.

I usually did most of my drinking at the beginning of the night anyway (intentionally so this would be a viable strategy), so I was mostly sobering up at the end.

But there were still plenty of nights where I slept on the host's couch or floor until morning, and a few times where I made poor decisions because I really, really didn't want to have to find other transportation (mostly just getting in the car with people who I couldn't determine if they were sober enough to drive). Taxis really are awful in small towns.