calculate CPU Over Commitment Ratio

Dear all

Hi

do you know how can use cpu-over-commitment?

i use this article

Testing vSphere 6.5 DRS – CPU Over Commitment Ratio – vMusketeers

my server is HP dl380 and has 2cpu with 10core = 20cpu

Totaly 7vcpu on my server is now use  (3vms) now i want power on other machine with 1vcpu

and set over-commit ratio to (8/20)*100=40 but when want to power.on that can not start machine and appear insufficient

resource even i set it to 100 and my vm could not power.on now how do i have to calculate this parameter?

BR

Babak