M-ratio
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In no-limit or pot limit poker, a player's M-ratio (also called "M number" or just "M") is a measure of the health of his chip stack as a function of the cost to play each round. In simple terms, a player can sit passively in the game, making only compulsory bets, for M laps of the dealer button before running out of chips. A high "M" means the player can afford to wait a number of rounds before making a move. A player with a low "M" must act soon or be weakened by the inability to force other players to fold with aggressive raises.
Invented by and named after Paul Magriel, the formula is:
For example, a player in an eight-player game with blinds of $50/$100, an ante of $10, and a stack of $2,300 has an M-ratio of 10:
That is, if the player only makes the compulsory bets, he will be "blinded out" of the game in 10 rounds, or 80 hands.
Poker player Dan Harrington studied the concept in great detail in "Harrington on Holdem: Volume II The Endgame", [1] defining several "zones" in which the M-ratio may fall:[2]
| M-ratio | Zone name | "Optimal" strategy |
|---|---|---|
| M ≥ 20 | Green | Most desirable situation, freedom to play conservatively or aggressively as you choose |
| 10 ≤ M < 20 | Yellow | Must take on more risk, hands containing small pairs and small suited connectors are useless |
| 5 ≤ M < 10 | Orange | Main focus is to be first in whatever you decide to play, preserve chips |
| 1 ≤ M < 5 | Red | Your only move is to move "all-in" |
| M < 1 | Dead | You are completely dependent on luck to survive |
