Measure the three ratios that describe a virtual estate: VMs per host, vCPU per core and allocated versus physical memory.
Three ratios describe an estate and they fail differently. VMs per host is a commercial number, vCPU per core is a scheduling number that only hurts once ready time rises, and the memory ratio is the hard one — above 1.0 the hypervisor is reclaiming, and beyond about 1.4 it is usually swapping. These are the numbers reported to management and used in licence negotiations, and each has a different failure mode — quoting only VMs per host hides whether the estate is one workload spike away from memory contention.
Virtualization Ratio
VMs per host = VMs ÷ hosts; vCPU per core = allocated vCPUs ÷ physical cores; memory ratio = allocated VM memory ÷ physical memory. The density score weights those 40/30/30 against healthy bands.
VMs per host = VMs ÷ hosts; vCPU per core = allocated vCPUs ÷ physical cores; memory ratio = allocated VM memory ÷ physical memory. The density score weights those 40/30/30 against healthy bands. Three ratios describe an estate and they fail differently. VMs per host is a commercial number, vCPU per core is a scheduling number that only hurts once ready time rises, and the memory ratio is the hard one — above 1.0 the hypervisor is reclaiming, and beyond about 1.4 it is usually swapping.
These are the numbers reported to management and used in licence negotiations, and each has a different failure mode — quoting only VMs per host hides whether the estate is one workload spike away from memory contention.
This calculator takes 7 inputs: Hypervisor hosts, Virtual machines, Total physical cores, Total vCPUs allocated, Total physical memory, Total memory allocated to VMs, Target VMs per host. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.