650c is a 26", close enough that most bikes made for one can take the other (as long as a rim swap goes with the deal.) I think 650b, which is smaller than 650c or 26", is called 27.5". 700c is 622, which is smaller than the old 27", but still it's referred to as 28". Why? I guess because 27" was already taken. It's kind of a meaningless to assign a size in a different system.