Okay, you've decided to bet. The question now is how much to bet. The size of your bet must accomplish two goals. The first is to disguise the strength (or if you are bluffing the weakness) of your hand. Secondly, your bet must tell a credible story. The purpose of betting, after all, is to tell a story designed to get your opponent to bend to your will. Do you want him to call, muck, or even raise? Your bet size goes a long way in accomplishing your goals at the table.
Let's break this into two categories. Pre-flop betting and post-flop betting in no-limit hold 'em. Because your bet size is limited in limit hold-em you have different decisions to make which is a topic for another time. In no-limit hold 'em, however, your decision making process and your bet size varies in these two conditions. Pre-flop betting should be sized relative to the big blind. If you are playing in a $2/$4 no-limit game and you are first to enter the pot you should bet between 2.5 and 3.5 times the big blind with the 3-bet being the standard raise. If you are first to enter the pot and your cards are strong enough to call from the position you are in then they are strong enough to raise. Calling gives you no information about your opponents while raising can tell you much about the strength of your opponent's hand.
Some people advocate that you size your bet based on your position at the table. If in early position raise 2.5x, in middle position raise 3x and in late position raise 3.5x. In early position, the argument goes, when you raise you are announcing a premium or very strong hand and a smaller bet with people acting behind you allows you to enter the pot cheaper than if you made a full standard raise. Because your bet size remains constant based on position and not on cards your opponents are left to guess what you hold.
Others argue that you should never vary the size of your pre-flop raise. If you decide that you will raise 3x the big blind then do so from every position with any cards within your range of hands for that position. Because your bet size never varies no matter where you sit relative to the button, they argue, you effectively disguise the strength of your hand.
I prefer a mixed approach that incorporates the random number generator described by "Action" Dan Harrington. In this approach, I decide that I will raise a standard 3-bets 75% of the time and 2.5-bets 25% of the time. I can, of course, vary that distribution or even add a 3rd variable to the mix if I wanted to do so. Now if I do this by counting my pre-flop raises so that every fourth raise was smaller by a half a bet I am not doing a good job of disguising my bet size at all. But, if I simply look at the second hand on my watch right before I bet, I can randomly vary my bet size. If the second hand is between 0 and 45 seconds I 3-bet. If it is between 45 and 60 seconds I bet 2.5 times the big blind. In this way, I reap the benefits of those advocating positional variance and those arguing for zero variance. My watch becomes an effective random number generator allowing me to mix up the size of my raise in any position thereby guaranteeing that I disguise the strength of my hole cards.
If the pot has been raised before the action comes to you there is a simple rule of thumb to remember; never call a raise with cards you would be comfortable opening with from your position. In other words, your cards must be at least one position earlier in your hand selection to call a raise in front of you. Of course, if the raiser is an opponent who enters too many pots raising you may want to adjust your play accordingly. On the other hand, if the raiser is a rock he deserves your respect and you may want to tighten up even more. Everything in poker depends on everything.
Post-flop presents a new condition. There is now an established pot. Betting pre-flop is made relative to the big blind while betting post-flop is based on a percentage of the pot. If you are telling a story that includes getting your opponents to call or raise you and you are first to act a standard raise now is between half and three-quarters of the pot. Let's say the pot is $10 on the flop. You are first to act holding AK and the flop came A72 rainbow. You have top pair and top kicker, most certainly the best hand at the moment. No flush draws, no straight draws and the board is raggedy. You want a call from anyone holding premium hands, small connectors which include at least one of the board cards. Sizing here is important. If you bet half the pot the pot is now $15. Your opponent is getting 3:1 from the pot. Any pair will give him the proper odds to call. If, on the other hand you bet $8, just slightly more than 3/4 of the pot, there is now $18 in the pot which is now offering a little more than 2.5:1 which may price your opponent out of the pot altogether. If you want a call then half the pot is a right sized bet. This same logic applies to the turn and the river.
I never ever vary my post-flop betting. I assess the purpose of my bet. Do I want a call? Do I want my opponent to raise which will allow me to trap by letting him do the betting for me on the turn and river? Do I want my opponent to go away? When I answer these questions I can make the proper decision to either bet for value or bet over aggressively.
A pot sized bet, the penultimate aggressive bet, creates the worst odds for your opponent because the pot is only offering 1:1 and unless he has a monster these are not odds to call. If you don't want a call then a pot sized bet accomplishes the same thing as an ultimate aggressive all-in bet without risking all of your chips, especially if your opponent has you covered.
Bet sizing goes a long way to support the story you want to tell during a hand. If you tell your story with guile and confidence then you're in the lead in the betting and you are forcing your opponents into making decisions and, therefore, mistakes. Remember, your profits come from your opponent's mistakes.
