No. Volt-amperes are apparent power, watts are real power, and every UPS publishes both because a load can reach either limit first. The watt figure is always the lower one and it is the one most often skipped.
Two units, one piece of equipment, and a difference that decides whether a UPS is big enough.
What each one measures
Volt-amperes are the product of the voltage supplied and the current drawn. They describe apparent power: everything the supply has to be able to deliver, including the part of the current that flows back and forth without doing work.
Watts describe real power: the part that is actually consumed by the equipment.
The ratio between them is the power factor, a property of the load rather than of the UPS. A load with a power factor of one draws the two figures equally; a load with a lower one draws more current than its consumption alone would suggest, and the supply has to carry that current regardless.
Why a UPS publishes both
Because it has two separate limits and either can be reached first. The inverter can only supply so much current, which is the volt-ampere limit; it can only deliver so much real power, which is the watt limit.
A load whose profile differs from the one the maker assumed can sit comfortably inside one figure and exceed the other. Sizing on the volt-ampere figure alone is the standard mistake, precisely because it is the flattering one.
How to use them when sizing
Add up the watts your equipment consumes, from the equipment makers’ published figures. Then find a UPS whose watt rating comfortably exceeds that total, and check that the volt-ampere rating is not the closer of the two constraints.
Leave headroom. A load close to either limit gives short runtime, runs the unit hard, and leaves nothing for the moment when every drive in an enclosure spins up at once.
Where else the distinction shows up
A runtime chart is normally drawn against load expressed as a proportion of one of the two ratings, and the maker states which. Reading a chart in the wrong unit produces an optimistic answer.
Power distribution units and rack strips publish limits in both units for the same reason.
And an enclosure’s own published consumption is in watts, which is the unit to keep the whole calculation in.
The line worth writing on the plan
Two ratings on the UPS, one consumption total for the load, and headroom on the tighter of the two. Everything else about a UPS — how it is installed, where it is placed, when its battery is replaced — comes from the manufacturer’s own instructions, and where those instructions touch the building’s wiring, that is work for somebody qualified.
The manufacturer’s own documentation comes first, and this page is not a substitute for it. Every rate, capacity, class figure, endurance rating, port speed and power figure on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A stated capacity is reported as the maker counts it, and is never restated in another unit, because the two are not the same figure. And for anything wired to the mains: a UPS and a surge protector are installed, sized and replaced as their own instructions say, and nowhere else. Volt-amperes are not watts, a stated runtime assumes a load the maker names, and a joule rating describes what a protection device absorbs before it stops protecting.
The questions that come up before an order
Why is the volt-ampere figure the one on the front of the box?
Because it is the larger number. It is not a dishonest one — it describes a real limit on what the unit can supply — but a purchase decided on it alone can exceed the watt limit while appearing to be within specification. Both figures are published, and a data sheet that gives only one is giving half the specification.
Do the same two figures appear on other equipment?
They appear anywhere alternating-current power is being supplied or consumed, including on generators and on some power distribution units. Equipment data sheets more often publish a consumption in watts, which is what you add up when sizing, and the UPS is where the two units meet.
Last reviewed 10 September 2026