Unfortunately, not. Without doing an assessment (e.g. by using Capacity Planner) everything would be more like "guessing" than "knowing". Without the details about CPU, memory and disk I/O usage it's nearly impossible to tell which hardware resources you are going to need.
In addition to this you need to think of high availability to ensure the 50 servers are available in case of a host/hardware failure. What kind of storage do you plan to use (local or shared, iSCSI or FC)?
I do not need HA in this moment. I am using FC disk for ESX host.
I just want to find document about how to calculate memory sizing generally.