Why 4xBB?
 

We all know that the standard opening pf raise in NL is 3-5xBB. I've wondered ever since I've started poker why this is the magic figure but have never really felt much of a need to voice the question.

Of course, I know that 2xbb is too small in that it offers too good implied odds. And that 10xbb is too much in that you wager too much to win too little. But I've never seen any sort of mathematical explanation as to why this is.

So that's it, has anyone seen any mathematical, logical, or otherwise non-laymans arguments for pre flop betting amounts?

Re: Why 4xBB?
 

Well, it depends on a whole lot of things, mostly the size of the pot, but also what your opponents are like and the average stack size in relation to the BB. 10xBB is surprisingly common in loose games with lots of limpers, especially if the stacks are deep.

I play primarily live micro-limit and generally try for something around a pot-size raise pre-flop regardless of what the big blind is. It may mean 3xBB in early position, or 10xBB in the blinds. I'm sure someone will come along with better strategy (and better reasoning) at a later hour, though.

Re: Why 4xBB?
 

Let's say you have AKo and I have a totally random hand. If you run a simulation you'll find that your AKo is about a 2:1 favorite over my random hand. You probably see where this is going . . . If you make a minimum raise you're offering me 1.75:1 on a call when I'm only a 2:1 dog. With position I should be tempted to call you without even looking at my cards. If I get a nice little pocket pair or something like 98s I'm priced in outright.

So the 3-5x BB raise is the "standard" because it offers poor odds to a caller, hopefully poor enough to make it difficult for them to make up the difference through implied odds, but the raise is small enough that if you are up against AA you don't lose all your profits on earlier hands.

Remember our true goal isn't to not get called - it's to have our opponents make a mistake either by folding a better hand or in the best case scenario to call us with improper odds.