Preflop Percentages

I was wondering where I could find a list of what has what % chance of winning preflop...like the %'s you see on tv when people are going at it? I found the heads up ones in HOH2 so I was wondering where a list of these were? Or are they they same? I know it depends on the amount of people but do you just have to memorize these or how are these calculated? After many trials, I figured that's how they got the numbers but I just wondered why for instance overpairs against smaller ones are 80-20 roughly? If there isn't a logical reason besides just doing the trials then so be it. Thanks!

http://poker-odds.flopturnriver.com/

The underpair makes a set just about 20% and rarely will make a 4 flush or straight, but will sometimes be beat by a higher set/flush etc.

Note that most TV broadcasts take into account the seen cards that have been folded, so they won't always match the real numbers.

When I started out I used this neat little program I found linked on FTR (somewhere in the strat guides). You can input pocket and board cards and let it simulate the outcomes on hundreds of thousands of tries, which gives very accurate percentages, even better than if you try to calculate them by hand (which I did too). The reason is that there often are things like backdoor flushes and board pairing etc that twitch the odds.

I remember in the first month I was constantly tabbing out of my poker game and inputting the hand/board configurations I had faced to see what the actual chances were. Now it's all automatic I think.