UPS Nightmare!

Onfortunately I was assigned a task to calculate the UPS requirement our network Equipments that includes the Routers,MUX,HUB,Switch.Now how do i calculate the number of UPS that I Will be needing? & many Standby time will those ups give me?.I triedthe APC selector but what it give's me is just how many UPS i need to buy. Can some one give me a solution out of this UPS nightmare.

Thanks,
WMW