For me, I can handle about 4 sapporo's, or a 6 pack of Keith's before I start feeling drunk. When it comes to hard liquor tho, I'm a sissy on everything except for tequila. Even one Jaeger bomb gets me tipsy.
For those that don't drink, you can just put yourself down for one, lol. Although I will say, my girlfriend is a non-drinker; gets wasted after downing a beer, but she puts back 4 Singapore Slings at the bar and walks fine.