The only accurate way to determine that is to determine the actual power usage. Your UPS may provide that information. All you can do is test the UPS. Start a game, which will maximize your power usage, and unplug the UPS. Verify that your PC continues to work. You could time how long your PC will remain on.i just want enough time to save my things and shut it down. i thought 850 va is enough to hold for at least 10 mins
That is true for US units. Many other countries do not include the USB interface on the UPS.An 850VA ups should have a usb output that may answer your question precisely after the software is installed.
Most cyberpower units of that size have a front display with that info.
What brand and model is the ups?
Max load 230 W (368 VA) on a 850mA UPS will last about 12 minutes
Normal usage 71W (113.6 VA) on a 850mA UPS will last about 70 minutes
Inverters may lower that by 0%, 10%, 25% or 35% which vary by manufacturer and typically can't be changed. As said above some units have that USB option to read power usage and the amount left provided you install the software. My UPS units are half that size and that gives me plenty of time to save and shut down.