The first step in calculating pot odds is knowing which cards you need to complete your hand. The simplest example of this is when you flop a flush draw. If you are playing Hold’em on 888.com and have two hearts in your hand and there are two on the board, that means that you have know that there are nine hearts (outs) remaining in the deck that complete your flush.
13 total suits – 4 exposed suit cards = 9
Now…with the other remaining board cards that don’t help you, you have knowledge of five cards in the deck. You now know that you are looking for nine hearts with 47 cards left. You then divide your outs by the remaining cards in the deck.
9 / 47 = 0.19 or 19%
Round that figure to the nearest five percent and you get 20%, which is also expressed as 1 out of 5 or 4:1, which is how pot odds are normally expressed.