If the pot is $10 and the guy bets $10 and is all in, you can call.

The pot is $20 when it gets to you. You have to call $10. Youre getting 2-1 odds on your money and you are approx 2-1 to hit your hand.

Dont forget that if the flop is King high and you have the nut flush draw, that means an ace might give you the winner so you could have 3 more outs.

Thats the simple answer.

If you want to think in terms of percentages you can also think like this. Add $10 to the pot, which is the size of the pot if you call. Calculate what 35% of that is or whatever your chance of making the draw is. That is your average share of the pot. If that share is bigger than the amount you need to call you are getting the correct odds to call.

So how big does the pot need to be in this case? You have to solve an equation to get the exact answer. Lets calculate the size of the pot when it doesn't matter if you call or fold. That is when your share of the pot is exactly as big as the size of your call. Let x be the pot size. You get the equation

0.35(x+10)=10.

Solve this

x+10=10/0.35=28.5 (approximately)

x=28.5-10=18.5.

If the pot is bigger than $18.50 you should call.

Hope this helps,
CipherJr

Very nice. Thanks guys. But that damn formula almost made my head explode.