Kris - I don't know of an explicit formula that will account for selections and expressions and yield a RAM utilization...however my understanding is that the server will continue to cache all new expressions and selection states up to the low working limit you set (in this case 80GB). This will often be much higher than the base app size plus concurrent usage load. Lots of selections and lots of distinct expressions adds up quick = the situation you describe. Once the working set limit is reached, the server cycles older items out of the cache and new selections and/or calculations are loaded into it. I think the short answer is your high RAM usage is not abnormal or a problem. The server is efficiently using as much RAM as you are allowing it to.