Couple of options, Arun.
That team can assist with sizing.
Contact a Cisco CSE (Consulting System Engineer) in your region. If you drop me an email (email@example.com) I can assist you in finding that resource for you.
Use our tool at :http://fwm.cisco.com
In that http://fwm.cisco.com/ site you will also be able to download our Sizing Guide.
I hope that helps.
RPS stands for Request per Second. So if the customer already have a Proxy or some tool that can provide the Peak HTTP/S request per second, that will help in sizing. Other wise go with the default suggested value