I need to add 8 additonal VMs to the current exsiting ESX servers.
Before adding the VM,i could like to know whether this esx can balance these VM.
Can anyone tell me how to do capacity planning.
You should already have installed or available VMware Guided Consolidation as part of Virtual Center if this physical.
There are other tools like VKernel Capacity Analyzer or Platespin Recon
you could also try Vkernel's capacity modeller , which is free.
http://www.vkernel.com/download/capacity-modeler