I don't play online, so correct me if I'm wrong, but online the standard raises are supposed to be somewhere around 3-4BB, right? This, of course, is based on sound principles, so it doesn't really change from table to table. The reason I point this out is you won't get wide fluctuations from table to table because most people online have at least a basic understanding of what a good opening size should be.
What the "standard" open live games vary WIDELY, even from table to table within the same casino. This past week at Wynn, I've been at 1/3 tables where the standard was 12-15 (4-5BB), and also where it was 20-25 (7-8BB).
The reason I mention this is that, in my opinion, at these stakes, whatever the "established" open at THAT TABLE is, the players pretty much stick to that area like lemmings. I'll see the same players be at a table where the "established" open is only 3BB, and then the next day the same guys are at a table where it's 9BB, and they, like little Lemmings, follow along.
Unfortunately, I've found that this means that I have to base my open around what the table considers "normal". Once I figure out the established open, then the question becomes, in this spot, do I want to go a little under or a little over? And sadly, this ALSO depends on table dynamics, because I've noticed that a sizeable chunk of live players respond to a bigger pre-flop raise than the "established one" by convincing themselves the player making the bet is bluffing because why else would he raise so much (so the correct think to do is flat with a marginal hand like KJo, of course) and there's also a sizeable chunk of players who arrive at the entirely opposite conclusion. Finally, there's a chunk of players who, once they've limped, aren't going to fold to pretty much any non-ridiciulous open, so even if you open to $20 at 1/2, some players are going to call. Get a table with this last category of playersd and no matter what you bet, you're likely getting called in 5 spots.
So long story short, I really think "it depends". Figure out what the "established" open is, and IMO, it's usually pretty clear what it is at that table that day, and also figure out how the players react to less than normal and more than normal opens (if they react differently at all). Once those facts are established, then bet appropriately based on whether you really want to make sure it gets to heads-up, or whether you're willing to risk (or you want) a 5-way pot.
Also, remember that most low-stakes live players don't think about bets in terms of BB or in terms of relative to the pot, but rather in terms of absolute dollars. The reason this matters for pre-flop raising is that if you decide to go larger/smaller than the established open, how much more/less has to be based on $, not on BB. If the established open is $14 at the 1/2 table that day, and most of the players are folding to bets bigger than that, if you've got AK and want to get it heads up by betting a size that the table will perceive as larger than normal, betting $18 probably won't do that - has to be more like $22.
Now a side question that's still relevant to the topic - if the established open at the table is an amount you don't like, and you want to see if you can change it by just consistenly being the guy who opens pre-flop and controls the action so that your number becomes the new standard - whether it's worth increasing the aggro to 11 neccessary to overcome the inertia of whatever number is already in their heads by repeating betting a different size until your size becomes accepted.