First check your host machine configuration and proceed.
Virtual CPU Limitations:
The maximum number of virtual CPUs that you can assign to a virtual machine depends on the number of logical CPUs on the host, the host license, and the type of guest operating system that is installed on the virtual machine.
Be aware of the following limitations:
■
A virtual machine cannot have more virtual CPUs than the number of logical cores on the host. The number of logical cores is equal to the number of physical cores if hyperthreading is disabled or two times that number if hyperthreading is enabled.
First check your host machine configuration and proceed.
Virtual CPU Limitations:
The maximum number of virtual CPUs that you can assign to a virtual machine depends on the number of logical CPUs on the host, the host license, and the type of guest operating system that is installed on the virtual machine.
Be aware of the following limitations:
■ A virtual machine cannot have more virtual CPUs than the number of logical cores on the host. The number of logical cores is equal to the number of physical cores if hyperthreading is disabled or two times that number if hyperthreading is enabled.
Check this link for your further clarifications.
From: VMware