What are outs in poker?
An out is an unseen card that can improve your hand. For example, if you hold four cards of the same suit after the flop, the nine remaining cards of that suit are usually counted as outs to a flush.
There are 47 unseen cards after the flop: 52 cards in the deck minus your two hole cards and the three community cards. Your opponents’ cards are part of those unseen cards, even though you cannot see them.
How to estimate poker odds with the rule of 2 and 4
With one card to come, multiply your number of outs by 2 for a quick percentage estimate. With both the turn and river to come, multiply by 4. This shortcut is useful at the table, but the exact chance is slightly different.
A flush draw with nine outs has about a 19% chance to hit on the turn (9 ÷ 47). If you can see both the turn and river, the chance to hit at least once is about 35%; the rule of 4 estimates roughly 36%.
Outs, odds and equity are different
Odds describe the chance of an event, while outs are the cards that may cause it. Equity is your share of the pot on average if the remaining cards are dealt, based on the hands or ranges being compared. Equity can include a share from split pots.
A draw can improve and still lose. An out is not always clean: a card that completes your flush could also give an opponent a full house, for example.
When the estimate can mislead
The rule of 2 and 4 assumes your outs really help and that the cards are still available. Discount outs that may leave you behind, and remember that an opponent can redraw on a later street. The shortcut also estimates card improvement, not whether calling a bet is worthwhile.
To compare a draw with the price of a call, see our guide to pot odds in poker. The starting hands guide explains how your two private cards begin a hand.