Does anyone know how to calculate UPS Power assuming I have server with 650 of watt.
Math is nice and all, but if you'd rather pick and choose from a list of equipment you might consider using the very nice UPS sizing tool from APC: http://www.apc.com/tools/ups_selector
I don't always purchase APC UPSs, but their selector tool can "do the math" for you and gives you some numbers in the end that can be applied to any UPS manufacturer's offerings (as well as, of course, some suggested APC products).
If you really want to know how much current your device is using I'd recommend using a clamp-on meter to test it. (You can certainly use something like a "Kill-a-watt" if you have it, too. The clamp on meters are nice because you don't have to disconnect anything.)