The ratio between girls and guys in a social situation. Just like any ratio, the Ham/Clam can be reduced. For example, if there are five girls and thirty guys at a party, the ratio is a poor 1:5 (See: Sausage Fest). A healthy ratio is 1:1 as there is the possibility that everybody's going to get hooked up; however, most males prefer a 2:1 ratio because... well, that's just awesome.
Trevor: Damn, this party is lame. It's all dudes!
Brad: Yeah, I'm estimating a 1:6 Ham/Clam ratio. Let's get out of here.
Ben: I'm liking the people we chill with, but we need to get a few more girls to even out the Ham/Clam.