You can find it just here
https://en.wikipedia.org/wiki/M-ratio
M=Stack/SB+BB+Total antes
For example
2300/50+10+10*8= 2300/230=10
According to Harrington
M Effective= M*(players/10)
9*(5/10)=4.5
This means that although the player's simple M value places him in the orange zone, his effective M dictates a shift in playing style appropriate for the red zone. In essence, ten times the effective M denotes the expected number of
hands a player can let pass before running out of chips.
Harrington further develops the concept to account for shortening tables, as is seen at the closing stages of multi-table tournaments. The M-ratio is simply multiplied by the percentage of players remaining at the table, assuming a ten-player table to be "full".