Originally posted by TheFrick
if a flush draw has 4:1 odds, the right call should me make only when the opponent bet 1/4 of the pot?
4:1 means 20% (in four cases you miss, in one case you hit), so your opponent would have to bet only 1/5 of the pot or less.
That being said, this only takes regular pot odds into account. You could potentially still make a call if your opponent bets more as long as you're getting the right implied odds, meaning that you could win enough money to make the call profitable in case you do hit.
This topic might be a little too complicated to describe in a couple of sentences, though, so I suggest you read the article on implied odds, if you're looking for more info on this.