Help with UPS!

Hey guys we are planning on replacing our old UPS because it only last for about 15 minutes during power outage.

The ff are the device load for the UPS:

5 IBM Servers (DC, File server, test server etc)
2 Switch
1 Firewall
1 Router
1 Modem
1 Monitor, Keyboard and Mouse
1 KVM switch
1 External HDD
1 Extra linux test server
(will add another device in the near future)

Can somebody recommend what vA should I need. I'm not very technical when it comes to this i cant even compute the load of the server. Based on the devices above, what is the best spec for a UPS preferably APC. Can somebody explain the volt ampere? will it last long if it's high? I need a UPS that will last 1-2 hours at least

Input is 220-240 v / 50-60 Hz and output is the same.

Thanks!

Have you check there in PowerTree. They have range of product.

And also this link helps to you. Gives a little explanation there.

Ok let me check thanks!

APC's site has a UPS selector tool that helps figure this kind of stuff out.
http://www.apc.com/tools/ups_selector/index.cfm