Ask LH: How Much Power Does My Desktop PC Really Need?

Hello Lifehacker, How does one work out how much power their computer needs? I’m really confused about this, so please explain how I can calculate how many watts my power supply unit (PSU) will need if I upgrade. And any other tips on choosing one? Thanks, Power Receiver

Dear PR,

Good question! Unless you’re building a ridiculously powerful gaming rig, you don’t need an especially beefy PSU. Unlike RAM and storage, it’s not a matter of getting the biggest you can afford. Having too much power will just be a waste of money and can also cause fluctuations in performance.

With that said, you don’t want the PSU to under deliver, either – this can cause your system to crap out when it reaches its maximum power output. In other words, you need a PSU with ample wattage for the job (as well as some extra for future-proofing) but without overdoing it.

As a general rule of thumb, you want around double the wattage your system draws on at full load for maximum efficiency. Most all-in-one desktops with a single video card will be able to get by on a 550 watt PSU.

However, that’s just a ballpark number – it really depends on the PC components you’re planning to use and their individual power demands. Some component models are specifically designed to have a low energy rating, while others, such as enthusiast-level GPUs, require more power than the average.

So it really depends on your particular build (which means you should choose your PSU last.)

The easiest way to get a tailor-made answer is to use an online PSU calculator. As their name implies, these apps calculate the wattage needed to power your system based on the components and system configuration you’ve chosen. (You can check out one example here.) Naturally, make sure to include your USB peripherals in the final tally.

Other things to look out for include the physical dimensions (will it actually fit inside your desktop chassis?), the PSU connectors/pins (are they supported by your motherboard/CPU?) and whether it has an “80 Plus” rating (this means that the power supply is certified to provide at least 80 per cent energy to the system when at 100 per cent load.)

In terms of specific brands, the quality-end of the market is stitched up by a handful of manufacturers, all of which provide similar bang-for-buck. Some brands worth considering include Corsair, Antec, XFX and Cooler Master. If you care about the noise your PC makes, keep an eye out for models with larger, thermally controlled fans for quieter operation.

Whatever you do, try to avoid cheap no-name offerings on Amazon and eBay – in addition to increasing the odds of an untimely PSU failure, you will also be putting your other components at risk. This is one occasion where it definitely pays to spend a little bit extra.



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