Alright, so I've been reading about pot odds for the past few days, and want to clarify that I am actually understanding the concept, and the steps involved in calculating the pot odds, so that if I am doing it wrong it can quickly be stopped and I can be guided in the proper direction.

So through the articles written here on flopturnriver I was able to find the percentages of completing a drawing hand.
1) With turn and river to come and 1-9 outs, then, (# of outs * 4) = approx. percentage of drawing one of your outs. And anything higher than 9 outs I know the percentage.
2) With only River to come, then, (# of outs * 2) + 1 = approx percentage of drawing one of your outs.

Now let's just for arguments sake say that with only 2 people in the pot after the flop I hold a nut flush draw. That means I have 9 outs and approximately a 36% chance of making my nut flush hand by the river. If the pot has $20 in it already, and I'm facing a bet of $18 do I have the proper odds to call?

Well here's where my question lies. After the $18 bet the pot is $38 and I'm needing to contribute another $18. Well when factoring pot odds do I use the total pot (including my call of the bet) or the pot (without my call) to determine whether a call is justified?

So essentially would I do this:

WIth $38 in the pot and a bet of $18 dollars to me I'm contributing 47.3% of the pot ($18 / $38 = .473). And the call would not be right because I'm contributing more that 36% of the pot.

OR

With $38 in the pot and a bet of $18 to me the pot will be $56 dollars after I call so I'm essentially looking at putting in $18 for a chance to win a $56 pot. So, I'm contributing 32% ( $18 / $56 = .32 )... and the call is correct to make.

Which is the proper way? Am I even close? And also when explaining please use percentages and not ratios. I just feel more comfortable with them if that's at all possible. Thank you and sorry if it was drawn out for a seemingly standard play. I just want to make sure I'm not on the wrong path and that I understand all I can.