Work out virtual machine density instantly with clear inputs, formula shown and shareable results.
VM density is the lower of the CPU and memory limits. CPU can be overcommitted — 4:1 vCPU to physical core is common for general workloads — but memory cannot be safely overcommitted without swapping, so it is usually the binding constraint. Reserving about 6 percent of RAM for the hypervisor is also necessary and frequently forgotten.
VM density
CPU limit = floor(cores x overcommit / vCPUs per VM); memory limit = floor((host RAM - hypervisor overhead) / VM RAM); density = min of the two
Because CPU cycles can be time-shared while memory pages cannot be shared without either ballooning or swapping, both of which degrade performance sharply.
Two to four times for general server workloads, one-to-one for latency-sensitive or licensed-by-core applications. Monitor CPU ready time or steal to validate.