I need help with odds calculation

[pocketBarns]

I'm looking to take my game to the next level. I do well in kitchen games and have recently started a regular poker group at my college, but I really want to improve. I see people talking about "knowing" that if there opponent is on a flush draw then they have only a 30% chance of winning, so give them 3:1 odds and stuff like that. I kind of understand what this concept is, but I don't understand how you get the 30%.

How do you calculate (or estimate) hand percentages, and could someone please elaborate just a little on the notation of "3:1", and how to arrive at the conclusion of those particular odds?

By the way, this is my first post, I have been lurking for a while and I really like the community. I hope to learn alot here, I've already picked up some useful tidbits.

[suitedaces84]

Is this what you were looking for? Also try the links on the left side there's useful information there.

Calculation your odds based on your outs is pretty simple but you usually won't have enough time to do it during a hand. I'd recommend memorizing the following for starters:
OESD--4.5:1
Gutshot--11:1
Four flush--4:1

[traz]

The 4/2 rule gives a rough estimate for on-the-fly calculations.

It works as such. When you see the flop, calculate the number of outs. Multiply this number by 4, and thats the percent of hitting on the turn OR river

Multiply by 2, and its only the odds of hitting on the turn.

For instance, if the flop has 2 hearts, and you hold 2 hearts, then there are 9 cards to complete your flush draw. You hold a 36% chance of completing it on the turn OR river...and an 18% chance of hitting it on the turn. Those are rough numbers, but close enough.

A 75% chance of winning would be a 3:1 ratio. A 25% chance of winning would be a 1:4 ratio.

A 30% chance of winnining is about 1:2.5 (closer to 1:2.3)