12,516 to average 20k. But to beat last year's R1 total, the crowd has to hit 21k on the dot. The equivalent Tigers home match last year managed 17,392.
Edit: officially 23,149 at the Rabbitohs game, not 23,500. So that makes 12,867 to average 20k and 21,351 to beat the 2009 R1 total.