In no-limit or pot-limit poker, a player's M-ratio (also called "M number", "M factor"[1] or just "M") is a measure of the health of a player's 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.
The concept applies primarily in tournament poker; in a cash game, a player can in principle manipulate their M at will, simply by purchasing more chips.
The M-ratio is calculated by the formula: 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, they will be "blinded out" of the game in 10 rounds, or 80 hands.
In essence, ten times the effective M denotes the expected number of hands a player can let pass before running out of chips.