Its better to get it from the horse's mouth, all you have to do is count the # of outs you need to make your hand (does not guarantee that making your hand will win you the pot). Once you have that, and you want to calculate the odds after the flop here's how you do it. Let's say you are in a common situation with a flush draw on the flop that you think will win if you hit it. You have 9 cards that will make your hand and two cards to hit it (13 of the suit, 2 in your hand 2 in the board or other combinations). Statistically you use a counterintuitive way to calculate this, you first ask your self, what is the probability that I will NOT hit the flush drawing two unknown cards and subtract that probability from 1 or 100%.
1 - (38/47 * 37/46) = 35.0%
From this you can calculate your pot odds needed to make this a wining call which is (100%/35.0% - 1) = 1.86 to 1
So if the raise is $50 and there is now $110 in the pot, you can call the raise. There are even implied odds that you can add to that if you think you will win additional money if you do hit the cards you need. You can change the formula to calculate the other odds as you see the numbers 38 and 37 in the formula is just the # of unknown cards - # of outs. The turn is much easier to calculate as it is just # of outs / 46 to get your percentage (about 20% on a flush draw meaning if there are 4 chips you will win to every 1 chip you call you will break even in the long run making these calls). Again, you can hit your flush and lose to the full house if you don't put your opponent on flopping a set, just a friendly reminder. Good luck!
Minnejohnny | 
Books or websites that discuss how to calculate odds properly 
