You have to realize that not all players (especially in low stakes games) use any kind of math in their decisions. There will always be a donk drawing to 4 cards (around 8%) on the river even if you played a hand to a tee and sometimes they will hit. There is a really good explanation of pot odds as well as hand odds at tightpoker . com / poker_odds(Sorry I do not have ten posts yet so I cant give you a direct link) . To determine pot odds, it is important to first understand hand odds. Also, it goes a little into implied odds which can be tricky if you are new to it.