UPS Sizing Calculator for NAS: What VA Rating Do You Need?
This calculator checks every UPS model on the list against your NAS and other devices: whether the load fits inside its VA and watt ratings, whether its runtime at that load (from the maker's own published runtime curve) covers the time your NAS needs to shut down, and whether it has the USB data port, output and outlets you need.
A UPS needs enough watts for the load, and enough runtime at that load for a safe shutdown. A bigger rating is not better if a smaller one already covers both. Models that fit are listed smallest rating first, with the reasons any other model does not.
It covers 5 UPS models sold in Australia whose makers publish a runtime curve. For another model, use its maker's runtime chart.
How the Sizing Works
Load. Your NAS's watts plus everything else on the UPS. A picked NAS uses its maker's busy figure, measured under the maker's own conditions, so it already includes its drives running.
Ratings. Each model's VA and watt ratings come from its maker's data sheet. The load must be no more than the watt rating. The VA rating is checked only when you enter a measured VA: NTK does not assume a power factor for your devices. A VA lower than the watts is not a possible reading for one load, so it is flagged and the VA is not checked.
Runtime. Each model's runtime at your load is read from the maker's published runtime curve (new, fully charged battery), the straight line between the two nearest published loads. NTK gives no figure outside the maker's data; below the lowest published load runtime is longer than the maker's figure there. That counts as covering your need only when that figure already does, and only as an inferred fit: it is labelled and listed after models with a published figure at your load. Under 15 W of total load NTK cannot tell for any model: Schneider says APC Back-UPS models with No-load Shutdown turned on switch off while on battery when the attached load is less than 15 watts, describing a Back-UPS that shuts down after 15 minutes on battery with backup time still left. It applies only to Back-UPS models whose user guide mentions the feature. (APC (Schneider Electric), checked 2026-10-14). NTK does not know which models here have such a cutoff, so it applies to every model.
Runtime you need = minutes on battery before the NAS starts shutting down + its shutdown time + any reserve.
Requirements. A model must also have what you tick: a USB data port (from the maker's specification), sine wave output, Australian outlets. Models that pass everything are listed smallest watt rating first. There is no single pick: the list says what each model does at your load.
UPS models checked
| Model | Rating | Output on battery | Outlets | USB data port | Battery | Warranty | Market price | Source |
|---|
| CyberPower UT650EG | 650 VA
360 W | simulated sine wave, line interactive | 3 Australian | No: None listed (no HID USB port, no management cable, no software) | Not user replaceable | 2 years (product), 2 years (battery) | $89
9 AU retailers, 2026-10-23 | CyberPower; CyberPower, checked 2026-10-08 |
| APC Back-UPS BX750MI-AZ | 750 VA
410 W | stepped approximation to a sine wave, line interactive | 3 Australian (AS/NZS 3112) | Yes: USB data port (PowerChute Personal Edition) | Not user replaceable | 2 years | $152
8 AU retailers, 2026-10-23 | APC (Schneider Electric); APC (Schneider Electric), checked 2026-10-08 |
| APC Back-UPS BX950MI-AZ | 950 VA
520 W | stepped approximation to a sine wave, line interactive | 4 Australian (AS/NZS 3112) | Yes: USB data port (PowerChute Personal Edition) | Not user replaceable | 2 years | $189
7 AU retailers, 2026-10-23 | APC (Schneider Electric); APC (Schneider Electric), checked 2026-10-08 |
| CyberPower VP1000ELCD | 1000 VA
550 W | simulated sine wave, line interactive | 3 Australian | Yes: 1 HID compliant USB port, USB cable, PowerPanel Personal | Not user replaceable | 2 years (product), 2 years (battery) | $179
10 AU retailers, 2026-10-23 | CyberPower; CyberPower, checked 2026-10-08 |
| APC Smart-UPS SMT1500IC | 1500 VA
1000 W | sine wave, line interactive | 8 IEC C13 (not Australian wall sockets) plus 2 IEC jumper cables | Yes: USB and serial ports, SmartConnect port (cloud monitoring) | Replaceable cartridge RBC7 | 3 years (UPS), 2 years (battery) | $1358
6 AU retailers, 2026-10-23 | APC (Schneider Electric); APC (Schneider Electric), checked 2026-10-08 |
Prices are the market price from NTK's index of current Australian retailer listings, with the date. A model without enough current listings shows no price. The makers' runtime points for each model are in the UPS Runtime Estimator.
Assumptions NTK made
Method last reviewed: 2026-10-14. UPS figures last checked at the makers' Australian sites: 2026-10-08. Market prices from: 2026-10-23.
Frequently Asked Questions
What size UPS do I need for my NAS?
One whose watt rating is above your total load, whose runtime at that load covers the time your NAS needs to shut down, and which has a data port your NAS can use. For a Synology DS1823xs+ at its 87.93 W Access figure, a 5 minute shutdown and a USB data port, the models that qualify are the BX750MI-AZ, BX950MI-AZ, VP1000ELCD and SMT1500IC. A bigger rating is not better if a smaller one already covers it. Add your router, switch and anything else on the UPS in the calculator.
How long will these UPS models run a NAS?
It depends on the total load on the UPS and on that model's runtime curve, which the maker publishes for a new, fully charged battery. Synology publishes 87.93 W (Access) for the DS1823xs+; at that load the maker's curves give about 16 min on the UT650EG, about 23 min on the BX750MI-AZ, about 28 min on the BX950MI-AZ and about 45 min on the VP1000ELCD. A smaller NAS can draw less than the lowest load a maker publishes: Synology publishes 28.25 W for the DS425+, below the 50 W where the UT650EG curve starts, so the estimator says only that runtime is longer than the 45 min the maker lists at 50 W. NTK counts that as covering a shutdown only as an inferred fit, listed after models with a published figure at the load. Under 15 W in total it cannot tell at all: Schneider says APC Back-UPS models with No-load Shutdown turned on switch off while on battery when the attached load is less than 15 watts, describing a Back-UPS that shuts down after 15 minutes on battery with backup time still left. It applies only to Back-UPS models whose user guide mentions the feature.
Why not just use the battery's watt hours?
Because runtime does not fall in step with load. CyberPower publishes 28 min at 60 W for the UT650EG but 3 min at 200 W: 3.3 times the load gives about a ninth of the runtime. A battery energy formula cannot show that, so NTK reads each model's published curve and joins neighbouring points with a straight line, the way the makers' charts do. Outside the published loads it gives no figure.
How much runtime do I need?
It varies from NAS to NAS, so time your own: start a shutdown and note how long it takes to power off. The tools start at 5 minutes, an NTK planning default, not a measurement. Runtime needed = the minutes on battery before the NAS starts shutting down + its shutdown time + any reserve you add. On a power failure a Synology NAS enters Standby Mode after a time you set or when the UPS is low on battery, whichever comes first.
How do I connect a UPS to my NAS for automatic shutdown?
The UPS tells the NAS the power is out over a data cable, usually USB. Synology DSM supports a UPS connected to the NAS by USB, a network UPS server (another Synology NAS sharing its USB UPS) and an SNMP UPS. Of the models here, the maker lists no USB data port for the UT650EG, so it cannot signal a NAS; the BX750MI-AZ, BX950MI-AZ, VP1000ELCD and SMT1500IC each have one. Synology says the UPS power off function varies by brand and model, some UPS devices do not support shutting down by DSM, and to run a power outage simulation test before relying on it. Check your NAS maker's UPS compatibility list for your exact model.
Does a NAS need a pure sine wave UPS?
NTK found no primary source saying a simulated sine wave harms a NAS power supply, so the tools state each model's output as its maker lists it: the UT650EG and VP1000ELCD output a simulated sine wave; the BX750MI-AZ and BX950MI-AZ output a stepped approximation to a sine wave; the SMT1500IC outputs a sine wave. If your NAS or power supply maker asks for sine wave output, tick that requirement in the UPS Sizing Calculator.
What is the difference between VA and watts on a UPS?
Each UPS has two limits on its data sheet, VA (volts times amps) and watts, and the load must stay inside both. For the BX750MI-AZ they are 750 VA and 410 W. A plug-in power meter shows the watts your devices draw; VA is higher when a power supply's power factor is below 1, and only a meter that shows VA can measure it, so the sizing calculator tests the VA limit only when you enter a measured VA. It does not assume a power factor.
When should I replace the UPS battery?
APC says the battery typically lasts three to five years, and that high temperatures, high humidity, poor quality mains power and frequent short discharges shorten its life. The makers list the battery in the UT650EG, BX750MI-AZ, BX950MI-AZ and VP1000ELCD as not user replaceable. The SMT1500IC takes the RBC7 replacement battery cartridge. The Back-UPS BX tests its battery automatically when it is turned on and every 14 days on line, and a long press of the power button runs a manual self test.
What warranty do these UPS models have?
The maker's own warranty, as listed on its page: the UT650EG 2 years (product), 2 years (battery); the BX750MI-AZ 2 years; the BX950MI-AZ 2 years; the VP1000ELCD 2 years (product), 2 years (battery); the SMT1500IC 3 years (UPS), 2 years (battery). Your first step for a faulty product is usually the retailer that sold it. The ACCC explains your rights under the Australian Consumer Law at accc.gov.au.
Which UPS models does the calculator include?
Five models sold in Australia with a published runtime curve: CyberPower UT650EG, APC Back-UPS BX750MI-AZ, APC Back-UPS BX950MI-AZ, CyberPower VP1000ELCD and APC Smart-UPS SMT1500IC. NTK checked each against the maker's Australian product page and recorded the date.
Where do the prices come from?
From NTK's market price index, built from current Australian retailer listings, with the number of retailers and the date. A model with too few current listings shows no price rather than an old one.