It is very difficult to estimate number of
Virtual Private Servers that can be installed on a single server. This is because there are too many factors involved. You need to consider server capacity in terms of memory, disk space and so forth, and also the configuration of individual Virtual Private Servers to determine the number of VPS's that could possibly run on a single server. You can have anywhere between hundred to thousand Virtual Private Servers built on a single server considering that the server resources are able to handle multiple
Virtual Machine instances. One has to keep in mind the probability of upgrades and ensure that every VPS is able to perform without hassles.