It depends what your raise is hoping to accomplish.
If you want to iso-raise and get some 70/3 fish to fold to your cbet on the flop then i raise 4xbb +1 for every limper
I woudnt raise anymore cause the way I see it is their calling or not and a couple BB's wont change their mind.
If they're going to call a big raise pf and then give up on most flops then let them, its money in the bank for you. Those players are exploitable b/c they call too much preflop and give up too often to a cbet on the flop, to maximise your exploitation of them you need to be getting them to put in a larger amount preflop.
Another reason to get more of their money in pf is that they will also tend to go to showdown and play big pots with less than adequate
hands, they dont understand the whole big hand big pot, small hand small pot idea, they over value their hands and are more than happy to go to sd for big pots with below par holdings.... so with some of your holdings your going to be raising 4xbb 5xbb for
value pf as it starts to build a big pot that their calling range isn't good enough to play for.
If your stealing when its been folded around from the BTN or CO against some 9/7, 12/4 nits in the blinds then raise it up 3xbb or even 2.5xbb because they won't be adjusting to your steals as well as they should be and a 3bb raise is going to accomplish the same thing that a 4bb raise would.
The size of your raises should be villain and situation dependant, don't get AK or w/e and just think, i'm going to raise 3xbb's here b/c thats the standard, think about what your raise is trying to do, are you raising for value, to steal, or to just isoloate a 70/10 fish, and change the size accordingly is my advice.