For St. Paddy’s Day I took my brother out to my favorite pub - his first time out to a proper bar. We had a couple beers, then moved on to another bar where we had a few more. I figure this is an introductory-level pub-crawl. A sample-size pub-crawl, if you will. So as I’m about to crash for the night, I’m wondering how other folks count their pub-crawls. It’s probably heavily dependent on the number of pubs and bars worth drinking in, in your locale. Any thoughts?
In my opinion there should be one drink per pub and the participants should be at least merry by the end. Depending on the tolerance of the drinkers this can mean as few as 5 or as high as 10 or more pubs in the crawl.
One drink per pub, in as many as you can fit in given the available time. In my town, that could involve at least 20 pubs and that’s before you get to the places you only go to if you’re absolutely desperate for a drink!
One drink per pub
You walk (or run or crawl), no vehicles can be involved
You cannot walk past a pub without stopping
These are now the core of my Official Rules. 
Does it HAVE to be one drink, or can it be at LEAST one drink per pub?
As the aim game is more about the number of pubs visited than the amount alcohol, then having a second at some time simply is self-handicapping.
Checking with a collegue who played a fair bit harder than myself, he made the point that it must be the same drink at each pub, and that if you started drinking two or more, that was the ante at every pub.
I use at least one drink per pub and at least 5 pubs as the basics for a pub crawl.
Of course, you can always tweak the rules for competetive pub crawling. Our group has organized Pub Crawl (American) Football. Everyone splits into two teams.
4 pubs = 4 quarters
1 beer/shot/mixed drink = 3 pts (field goal)
Irish Car Bomb = 6 pts (touchdown)
If a few of us moved on through 3+ pubs in an evening, especially in an ad hoc “lets see what the next place is like” sort of way, I’d start to describe it as a pub crawl.
Contrariwise, if I set out to have a pub crawl, I’d mean an “as many pubs as possible” sort of thing, which would probably involve having one drink in a series of pubs on a specific route, or similar.