Calculate "outs"

I posted this in the "Theory" section and got no help. Maybe it will be better here.

Someone told me how to quickly calculate approximate odds on my "outs" after the flop. I remember that with only the river remaining, I multiply my outs by 2, and add 1. Example: I have pocket Kings, Villain has pocket Aces. Flop and turn are blanks, leaving me two outs (the remaining kings), hence, 2 kings x 2= 4. Add 1= 5. I have a 5% chance of hitting an out. My question is regarding when I still have the turn and river remaining. I think it was something like multiply by 3 and add 2, but I can't remember. Will someone please let me know how to figure the odds when there are two cards still to be seen?

Thanks.