UPS units are sold in VA; your equipment is rated in watts. They are not the same thing, and the gap between them is why a “1100VA” UPS does not run 1100 W of load. Convert either way here.
Why VA and watts differ
VA is apparent power — volts multiplied by amps. Watts is real power, the part that actually does work. The ratio between them is the power factor. For the APC Back-UPS families that ratio is around 0.6, so an 1100VA unit supports roughly 660 W. Online Smart-UPS units run nearer 0.9, which is why a 1 kVA online unit carries far more real load than a 1000VA line-interactive one.
When you are sizing, always work in watts first, then convert to VA at the end. Comparing a watt figure against a VA rating is the most common way people end up with a UPS that is too small.
Other tools
Frequently asked questions
How do I convert VA to watts?
Multiply the VA rating by the power factor. For APC Back-UPS and other line-interactive units that is about 0.6, so 1100VA is roughly 660 W. For online Smart-UPS units it is nearer 0.9. The converter on this page does it either way.
Why is a 1100VA UPS not 1100 watts?
VA is apparent power and watts is real power; the ratio between them is the power factor. A UPS is sold on its VA rating, but the load you can actually connect is the watt figure, which is always lower. This is the most common sizing mistake.
Should I size a UPS in VA or watts?
Work in watts, because that is what your equipment draws, and convert to VA only at the end to pick a model. Comparing a watt figure directly against a VA rating is how people end up with a UPS that is too small.