It's somewhat complicated and you have to know each player's standard deviation in their ratings. There's probably a direct calculation in the stats book. But I've built a simulator that generates 1000 random scores on a bell curve for 1 to 30 people using their SD values. Then just looks at the scores and figures who won. For example, a player with a 1033 rating and an SD of 23.7 will beat a player with a 1013 rating and SD of 29.5 72% of the time if they are playing head-to-head. Can't help beyond that.
Rater of the tossed arc.