Quote:
Originally Posted by Tyrober
Its just standard...
Not a great answer. There's some good maths reasoning behind it.
Basically you want to raise enough to narrow your opponents' range (ie, fold out random trash which can be really difficult to play against post-flop), but not so much that you get rid of every hand except ones that beat you.
Actually different raise sizes for different strength hands would be more correct mathematically, but since that would tell people how strong your hand is, it's not a good idea in practice - which is why people tend to use a standard raise (or one based on other things than hand strength, such as position or effective stacks).
A min-raise of 2bb encourages the big blind to call with a very wide range (not as wide as limping, ofc, but still pretty wide). And a raise of >5bb puts a lot of pressure on your hand to succeed. So 2-5bb is good.
Then it makes sense to make the smallest raise you can to get the job done. For 100bb effective stack cash games, 3bb is effective but not too expensive. People are not going to change their behaviour much if you put in 4bb instead, so why waste the extra chips? The less you put in each time, the more often you can do it for the same cost.
A lot of people raise a lower amount on the button for that reason. Button raises get less respect and are 3bet more often, so it makes sense to make them cheap. Also, as Daniel Negreanu says: you don't mind if the blinds call out of position, right?
3bb turns out to be a nice standard raise size because of the maths, and that's why the thinking players do it, why books recommend it, and why it has become standard. Just because most people just do it because everyone else does, or because they read it somewhere, doesn't make that the
reason for it.