What's the Probability of hitting the board on the Turn or the River

I've been looking for the answer to this for a while. I have my lovely Ace-King and I missed the flop. The flop is 9 5 2 rainbow. For several reasons, I put my opponent for a top pair (9 - kicker) or a pocket pair in hand (Jacks or eights...etc.). I know that in order for me to win (in showdown), I'll need to hit the board on the turn or more ironically on the river. What's the percentage for that to happen (hitting A or K on turn or river)? How often do pro players generally draw for this?

• Please unaccept this accepted answer. Lee Daniel Crocker is correct. Oct 15 '15 at 4:40

Sometimes during play you want a quicker method that isn't 100% but gives you very close percentages.

The rule of 2 and 4.

If you have 2 cards left to reveal (ie the turn & river) then you multiply your outs by 4.

If you have 1 cards left to reveal (ie just the river) then you multiply your outs by 2.

So in your example, 6 outs with 2 chances left = about 24%.