Sorry to resurrect an old thread, but I can't seem to find the other (and longer) UPS thread I read a few months back.

I used the apc calculator recommended above. I'm just wondering how come it doesn't ask for the other pc parts like video card, no. of fans. etc.-- aren't they important in calculating for the power requirement?

Also, the best price recommendation I got was APC BACK-UPS RS 800VA 230V. Run time of 17 mins. I don't need it to be that long. I just need around 5 mins to shut down. Is it safe to assume I can opt for the 650VA?