What Size UPS Do You Need for a Gaming PC? Watts, VA and Runtime

By James Thompson · Updated: 15 October 2026

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Size a UPS from the equipment you will plug into its battery-backed sockets. Add the PC’s wall demand, the screen you need to save your work and any essential network kit, then allow power headroom and enough battery time to shut down. The wattage printed on the PC’s PSU is a different number: it describes the PSU’s output capacity.

For a smaller British-socket setup, start with APC BE850G2-UK. For a heavier desk load with IEC leads, compare APC BR1500GI. The UPS buying guide explains those routes and the pure-sine alternative; the calculation below tells you which capacity to shortlist.

Measure the equipment you want to keep running

Use a suitable plug-in power meter, or the UPS’s own load display once installed, to record wall demand. Take readings during the work that matters: a demanding game, a render or a sustained CPU task. A quiet desktop reading will understate a machine that spends its evenings gaming. Include the monitor separately if the meter only measures the tower.

An 850W PSU does not mean the PC continuously draws 850W. Its rating is the DC capacity available to the components; mains demand also includes conversion losses. The PC power-supply guide explains that role. For UPS sizing, work from the complete machine’s AC input rather than adding a GPU specification to a CPU specification.

Write down what is on each protected socket. One monitor may be enough to save and exit; the second screen, speakers and decorative lighting can remain outside the battery budget. Keep the switch on battery if your PC or NAS needs it for shutdown messages.

Keep watts and VA as two separate checks

A UPS has a watt limit and a VA limit. Watts describe real power; VA describes apparent power. Both limits must cover the attached load. Power factor links the two: VA = watts ÷ power factor. Use the equipment’s measured or documented power factor, rather than assigning every device the same value.

Do not calculate a universal watt capacity by multiplying every UPS’s VA label by 0.6. The actual manufacturer rating decides. In this shortlist, the BE850G2-UK is 850VA/520W, while the BR1500GI is 1500VA/865W. A VA number by itself cannot tell you whether a particular model has enough watt capacity.

Work through a complete desk example

Here is an illustrative desk calculation using assumed wall readings. It is a worksheet, not a benchmark for a particular processor or graphics card.

Using 25% watt headroom gives 460 × 1.25 = 575W. Schneider’s selection guidance recommends headroom; 25% is the planning allowance used in this example. The 520W BE850G2-UK cannot provide that allowance. The 865W BR1500GI passes this watt-capacity check, leaving waveform, VA and runtime to assess.

If the combined load’s power factor were 0.9, its apparent power would be about 511VA: 460 ÷ 0.9. Applying the same illustrative 25% reserve gives about 639VA. Replace that assumed factor with the real load data when choosing equipment. Adding VA headroom does not increase the UPS’s separate watt rating.

Choose runtime around the shutdown job

Decide what the battery needs to achieve. At a desk, I would prioritise time to save the current work, close the application and complete shutdown. If the goal is keeping a router alive through a longer interruption, size that low-load arrangement separately rather than leaving a gaming tower consuming the same battery.

Use the exact UPS’s runtime curve at the expected load. A quoted runtime at half load is not the runtime at your calculated load. Battery condition and temperature also affect the result; an old battery can still report fully charged while offering less useful runtime.

For a shared PC and NAS setup, the NAS may need to stop services and unmount storage after the PC exits. Add that sequence to your required time, including a reserve for a slower shutdown. The NAS UPS shutdown guide covers the communication path and restart checks.

A watt rating describes power capacity, not stored energy. A larger VA label does not prove a longer runtime at the same desk load. Compare the manufacturers’ curves directly, and look for supported battery-expansion options only when extended operation is part of the job.