What UPS rating do you need?

Q: What is the difference between the VA and the watts of a UPS?

Watts are the power your devices actually draw; VA (volt-amperes) are the apparent power the UPS can supply. The two are not equal: the ratio between them is the power factor, somewhere between 0.6 on entry-level models and 0.9 on a recent on-line unit. A UPS advertised as “1,500 VA” may therefore deliver only 900 W. This is the most common sizing mistake.

Q: How long does a UPS last during a power cut?

A few minutes in normal use, and that is by design: a UPS is there so you can save your work and shut down cleanly, not so you can carry on working. To ride out a long cut you need specific sizing with additional batteries — request a quote.

Q: Can the UPS battery be replaced?

Yes, and it is a consumable: it ages over three to five years, far faster in a hot room. A UPS with a dead battery keeps supplying power in normal times and no longer protects anything during a cut — with nothing obvious to warn you. See the UPS batteries.

Tick what you want to protect. We add up the wattage, apply the safety margin, convert to VA and tell you the rating to aim for. A “1,500 VA” UPS does not deliver 1,500 W — that is the whole difficulty of this calculation, and it is exactly what this tool does.

Desktop PC
≈ 200 W · tower only
0
High-performance desktop PC
≈ 400 W · dedicated graphics card
0
Monitor
≈ 35 W
0
Laptop
≈ 65 W · with its charger
0
Inkjet all-in-one
≈ 30 W
0
NAS
≈ 60 W · 2 to 4 drives
0
Tower server
≈ 400 W
0
Rack server
≈ 600 W
0
Network switch
≈ 30 W
0
PoE switch
≈ 150 W · powered cameras included
0
Router, modem or access point
≈ 20 W
0
Video recorder (NVR/DVR)
≈ 60 W
0
Till or point-of-sale terminal
≈ 80 W
0
IP telephone system
≈ 40 W
0

The most common cases, already worked out

What you are protecting	Power	With margin	Recommended UPS
One workstation (PC + monitor)	235 W	306 W → 510 VA	650 VA
One high-performance workstation (PC + 2 monitors)	470 W	611 W → 1019 VA	1,500 VA
A small network setup (router, switch, NAS)	110 W	143 W → 239 VA	650 VA
A CCTV recorder and a PoE switch	210 W	273 W → 455 VA	650 VA
A shop till (POS + receipt printer)	110 W	143 W → 239 VA	650 VA
A tower server and its monitor	435 W	566 W → 944 VA	1,000 VA (1 kVA)
A small rack (rack server, switch, NAS)	690 W	897 W → 1495 VA	1,500 VA

Reference power figures

Typical figures in operation, deliberately taken at the top of each range: we are sizing protection, not an electricity bill.

Equipment	Power used
Desktop PC — tower only	200 W
High-performance desktop PC — dedicated graphics card	400 W
Monitor	35 W
Laptop — with its charger	65 W
Inkjet all-in-one	30 W
NAS — 2 to 4 drives	60 W
Tower server	400 W
Rack server	600 W
Network switch	30 W
PoE switch — powered cameras included	150 W
Router, modem or access point	20 W
Video recorder (NVR/DVR)	60 W
Till or point-of-sale terminal	80 W
IP telephone system	40 W

Our UPS ratings

Frequently asked questions

What is the difference between the VA and the watts of a UPS?

Watts are the power your devices actually draw; VA (volt-amperes) are the apparent power the UPS can supply. The two are not equal: the ratio between them is the power factor, somewhere between 0.6 on entry-level models and 0.9 on a recent on-line unit. A UPS advertised as “1,500 VA” may therefore deliver only 900 W. This is the most common sizing mistake.

Should you allow a margin on the power?

Yes, at least 30 %. It covers three things: the current surge when devices start up, the battery losing capacity as it ages — very quickly in an unconditioned room — and room for a future device. A UPS loaded to 100 % lasts a few seconds and wears out fast.

Can you plug a laser printer into a UPS?

No. The fuser of a laser printer draws a very high current in bursts, which trips the UPS or wears it out prematurely. The same goes for a heater, an air conditioner or any resistive appliance. A UPS is for IT equipment: tower, monitor, network gear, recorder, server. See our UPS guide.

How long does a UPS last during a power cut?

A few minutes in normal use, and that is by design: a UPS is there so you can save your work and shut down cleanly, not so you can carry on working. To ride out a long cut you need specific sizing with additional batteries — request a quote.

Off-line, line-interactive or on-line: which one to choose?

In Morocco, the daily plague is not so much the outright power cut as voltage fluctuation and micro-cuts, which wear out power supplies. That is why line-interactive, with its automatic voltage regulation, is the sensible minimum for equipment of any value. On-line double conversion is a must for a server, a rack or sensitive equipment.

Can the UPS battery be replaced?

Yes, and it is a consumable: it ages over three to five years, far faster in a hot room. A UPS with a dead battery keeps supplying power in normal times and no longer protects anything during a cut — with nothing obvious to warn you. See the UPS batteries.

To understand topologies, waveform and battery life, read our UPS guide. For a rack or a laboratory, ask us to size it for you.

What UPS rating do you need?

The most common cases, already worked out

Reference power figures

Our UPS ratings

Frequently asked questions

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