cards in deck - known cards = remaining unknown cards

outs/remaining unknown cards =

odds of hitting.

you can also do the rule of 2 and 4, which is a quick calculation for figuring out the odds of you hitting on each street or the odds of hitting on either street.

- outs * 2 to calculate your flop-to-turn, and the turn-to-river odds separately.
- outs * 4 to calculate your odds for hitting on either the turn or river.

it's important to note that you only use the rule of 4 if you're guaranteed to see the river, which only happens if it's guaranteed you will not face any more betting rounds post flop. otherwise, you'll be calculating the wrong odds to for the flop to turn as there is the possibility of you folding on a turn-to-river bet. the only exception to this is if effective stacks are so shallow that you're guaranteed to call a turn bet no matter what hits. majority of the time, though, you'll be using the rule of 2.

going slightly further, the rule of 2 and 4 is very close but not exactly perfect. if you aren't a stickler for being exact, as long as you're over the

pot odds with the hand odds (using percentage method), then you'll be fine.