Preflop is the most common street, so it pays to put some thought into it instead of using the same sizes as everyone else. Here are some tips for choosing a good RFI size:

1. Big sizes maximise value the times we get called by the BB
As the aggressor, we have an equity advantage on most boards. This is especially true vs the BB, who is calling a weak and wide range. A big RFI size (such as 3x) magnifies our edge, bloating the pot in a situation where we have the upper hand.

2. Small sizes save us money the times we get 3bet
A big part of our raising range is 0 EV against a 3bet—especially if the 3bettor is in position. A smaller RFI size (such as a minraise) saves us money the times this happens.

Consequently, our RFI size depends on the ratio of 3bets to calls that we expect to face. In small stakes live games for example, we can afford to make huge raises (often >5bb) because the player pool is calling too wide, and not 3betting enough. The ratio of 3bets to calls is low, so our priority is to make the pot as big as possible the times we get called.

3. Position matters
Contrary to popular belief, we actually raise smaller from early position, despite the fact that our range is tighter. Watch this short video to find out why:
The Magic RFI Size (2min)