Actually previous rule was in each sleeper coach 6 berths were reserved for RAC. In 12811 there is 13 SL, so in 1 coach 12 RAC holders, so in 13 coach 13*12 = 156 RAC. But now seems increased RAC count has been implemented. So now according to previous notification, 7 berths are being used. So now total RAC is 13*7*2 = 182 RAC.