You should measure your PC's power consumption on the primary side, i.e. from the wall, not trust software readings that don't account for the PSU's efficiency and some other factors. Do so under full load (e.g. Prime95, FurMark, OCCT or similar) to account for spikes in power consumption and to give the UPS enough headroom.
Also keep in mind that you likely need a monitor, a router (and/or network switch) and maybe other (peripheral) devices in case of a power outage. Meaning you should see what they pull from the wall and add that to your PC's power consumption - and connect them to the UPS, of course.