Calculate overcommitment ratio of a host from vSphere Client

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

Overcommitment ratio represents the resource allocation status on an ESXi host. The ratio is not shown in the UI. However it can be calculated manually from the data in UI.

Resolution

1. Open vSphere Client.
2. Click the ESXi host in inventory.
3. Click "VMs" to visit VM view.
4. Click the drop down menu and select "Advanced Filter". Click "ADD NEW". Change filter to "State". Select "Powered On", click "APPLY".
5. Click "Manage Columns". Select "Memory Size" and "CPUs". The allocated memory and CPU count will be seen at right columns. 
6. Calculate the total allocated CPU count and memory. (Optional) Click "Export" to generate a sheet, add numbers up with a sum function.
7. Calculate the overcommitment ratio for CPU and memory.
   
   
   

    The CPU overcommitment ratio determines how many virtual CPUs (vCPUs) are contending for each physical CPU core (pCPU). While hyperthreading provides logical CPUs (lCPUs), the standard and conservative baseline for CPU overcommitment calculations relies on physical cores to ensure performance predictability.

   Formula:

   Ratio = ∑ vCPU  ⁄  pCPU

   • vCPU: Total number of virtual CPUs assigned to all powered-on virtual machines on the host.

   • pCPU: Total number of physical cores available on the ESXi host (Sockets × Cores per Socket).

   
   

   The memory overcommitment ratio measures the total allocated virtual memory (vRAM) against the physical host memory (pRAM). ESXi uses memory reclamation techniques (Transparent Page Sharing, Ballooning, Memory Compression, and Host Swapping) to manage this overcommitment.

   Formula:

   Ratio = ∑ vRAM  ⁄  pRAM

   • vRAM: Total memory configured for all powered-on virtual machines.

   • pRAM: Total physical memory installed and addressable on the host.