AFAIK it's 1point per person in the group.
And if you win the roll, and got to say something, you get an extra 1 point per person in the group.
So loosing the roll: Points= number of people in the group
Win the roll: Points = number of people in the group x 2
2 person group
2 for the loser, 4 for the winner
3 person group
3 for each loser, 6 to the winner
4 person group
4 for each loser, 8 for the winner