As with many server performance questions, the answer to this question is “it depends”. You can run as many VMs on a single host as your hypervisor supports (usually that is a lot) and as you have server resources for (RAM, CPU, Disk, and Network).
Typically, on a desktop PC, you can run 1-3 VMs and on a Server you can run 10-50 VMs – depending on the application demands.