The 4 x 2 rule is perhaps one of the most valuable heuristics you can use at the poker table. You can choose from a wide selection of poker tools which overlay your table online and give you the probability of making your hand, but what happens when you're playing real poker? How are you going to remember the odds? Well, experience is a major factor, you'll find over time that the odds just become ingrained naturally. And there's nothing wrong in learning the true odds from a bit of paper parrot fashion, but this can be quite laborious. Luckily help is on hand in the form of the 4 x 2 rule.
To calculate the % chance of making you hand on the turn and the river, just take the number of outs you have post flop and multiply it by 4, this will give you an approximate % if making your hand. For example: you hold Ks,9s and the flop comes 6s,2s,Ad and you suspect someone has an ace, this leaves you with 9 spades to make your hand. So, 9 x 4 = 36% meaning you're slightly better that 2/1 to make you hand on the turn and river Combined. This is an approximated figure, your actual probability is 35% to make your hand, but as you can see it's close enough.
To calculate the % chance of making you hand on the next card dealt, either be it on the turn, or the river all you do is take your number of outs and multiply it by 2. For example with an open-ended straight draw the odds of making your hand on the next card dealt would be 8 x 2 = 16%. Again, this is an approximate figure, the true probability is actually 17%.
This is an easy and reliable method of getting you within the 1-2% margin of error for calculating the odds of making your hand.
Revised 4 x 2 Rule
For a more accurate measurement of making your hand than the normal 4 x 2 rule, use the following method:
- For Turn & River: (Outs x 4) - 1%
- For Next Card Dealt: (Outs x 2) + 1%
This will give you a margin of error of less than 1%