http://www.pokerstrategy.com/strategy/bss/1535/1/
it says:
How much should you raise?
IF THERE WAS NO RAISE BEFORE YOU
If no one raised before you, you simply raise 4 big blinds + 1 big blind for every player that entered the hand before you.
Your raise =
4x big blind
plus 1 big blind for every player that entered the hand before you.
so the question is WHY 4x ? Why not 2.5x?
Cos it's either outdated or simply wrong ♦ Most ppl raise 3x from all of the positions except for btn ( sometimes CO) where they raise 2.5x or 2x even
Hi Balltas,
This is one of the older articles. Back then, raising 4x was considered the optimal strategy against the player field of the time.
While I have come across people who still advocate raising 4x, I think it is better in today's games to raise 3x or 2.5x, depending on your position and other factors, instead. This is also what seems to be suggested in most of the strategy courses I have visited this year.
If you play nl2 like me, I would stick to 4x because people like to 3bet so much on 3x raises, so 4x makes it harder for people to steal your raises IMO.
the general idea is, the more value heavy your range is, the bigger you should raise. "wrong" or "right" are too strong terms 
cats
english blog: Never deposit - ZOOM poker (i'm back! ...maybe)
