[ottsville]

In general, the thought around here is 3xbb plus 1bb per limper. Many advocate an extra bb or two if you are raising OOP.

If you simply raise 3xbb regardless of position and limpers in front, you will often be giving good odds for someone to call you. Let's say the game is 10nl, you are in CO with a raising hand and four people have limped already. You raise 3xbb; the pot is now $.85(4 limpers, blinds, and your raise). Let's say button and sb fold...the big blind is getting ~4:1 immediate odds(and with each call the next limper gets better odds). Lots of players will call this small raise and try to outflop you.

Now, if you raise 3xbb + 1bb/limper, your raise will be to $.70 and the pot will be $1.25. The bb will be getting about 2:1 on a call and will need a much stronger hand to call. Some raising hands can handle more callers, but even AA holds up a lot less the more players you have in the pot.

There's lots of other factors to consider - meta game things, opponents behind, opponents already in pot, stack sizes, etc, but the 3xbb plus 1bb limper should serve you well as a starting ground.