Do I understand UPS power correctly?

Hey all,

Building out my lab, I was going to get a rackmount UPS. The one I'm looking at is a Cyberpower OR1500LCDRM1U. It says it offers:

1500 VA, 900 W, 120 V

Do I understand correctly that all I need to do is find the Wattage rating for each of the components I want to plug in and add them up? My components right now are pretty light, only about 120 watts total. But soon I'm going to expand and build out a Nutanix CE cluster with 3 nodes and a rack of drives. I was looking at using some NUCs but they are each rated at 330W.

So that would mean even the NUCs by themselves would over-provision the UPS right? Then on top of that I would still need all the other equipment in the rack to be powered.

Am I understanding this correctly or is there something I'm missing?