Converting between CPU summation and CPU % ready values
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Converting between CPU summation and CPU % ready values


Article ID: 306576


Updated On:


VMware vCenter Server VMware vSphere ESXi


Some documents, such as VMware's whitepaper Performance Troubleshooting for vSphere 4.1 refer to the CPU ready value as a summation value. Other documents, such as the vSphere Datacenter Administration Guide, refer to the CPU ready value as a percentage value. Therefore, you may need to convert between CPU ready summation and CPU ready percentage values to troubleshoot some performance issues.


To convert between the CPU ready summation value in vCenter's performance charts and the CPU ready % value that you see in esxtop, you must use a formula.

The formula requires you to know the default update intervals for the performance charts. These are the default update intervals for each chart:

  • Realtime: 20 seconds
  • Past Day: 5 minutes (300 seconds)
  • Past Week: 30 minutes (1800 seconds)
  • Past Month: 2 hours (7200 seconds)
  • Past Year: 1 day (86400 seconds)

CPU ready %

To calculate the CPU ready % from the CPU ready summation value, use this formula:

(CPU summation value / (<chart default update interval in seconds> * 1000)) * 100 = CPU ready %

For example:

The Realtime stats for a virtual machine in vCenter might have an average CPU ready summation value of 1000. Use the appropriate values with the formula to get the CPU ready %.

(1000 / (20s * 1000)) * 100 = 5% CPU ready

CPU ready summation value

To convert the CPU ready % into a CPU ready summation value, reverse the calculation and use this formula:

(CPU ready % / 100) * <chart default update interval> * 1000 = CPU summation value

For example:

If a virtual machine has a CPU ready % of 5m, its CPU ready summation value on the Realtime performance chart is calculated like this:

(5 / 100) * 20s * 1000 = 1000 CPU ready
Note: The result of above calculations are a sum of each virtual CPUs %RDY time. Individual core Ready time can be roughly estimated by dividing by the number of cores. However, it is more accurate to go by the vCPU metrics themselves. vCPU metrics are only collected in realtime by default.

Additional Information

CPU ready %

As a shortcut, you can use the following formulas for the default chart update intervals to get the CPU ready %:

  • Realtime: CPU summation value / 200
  • Past Day: CPU summation value / 3000
  • Past Week: CPU summation value / 18000
  • Past Month: CPU summation value / 72000
  • Past Year: CPU summation value / 864000

Example: A realtime CPU summation value of 1000 is divided by 200 to give a CPU ready % of 5.

CPU ready summation value

As with the longer version of the formula, reverse the formula and multiply (rather tha dividing) to calculate the CPU ready summation value:
  • Realtime: CPU ready % * 200
  • Past Day: CPU ready % * 3000
  • Past Week: CPU ready % * 18000
  • Past Month: CPU ready % * 72000
  • Past Year: CPU ready % * 864000
Example: If you have a CPU ready % 5, multiply it by 200 to get a Realtime CPU ready summation value of 1000.
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