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Tools

PSU calculator

Choose your processor and graphics card, say what else is in the PC, and we work out how much power it draws and which wattage to buy. Then we list the cheapest power supplies in stock at that size.

Start with your graphics card and processor. Those two account for most of what a PC draws.

How this is worked out

The processor and graphics card are read from the power figure on their VantaSpec page (TDP), or from our table of published figures for that model when the page has none. For processors we use peak power, not the label figure, because a chip labelled 125W can pull over 250W under load. We add 80W for the motherboard, memory, a drive and fans, plus a few watts for each extra stick, drive, fan or liquid cooler pump. Then we multiply by 1.5 and round up to the next 50W: power supplies run best at around half load, and modern graphics cards spike far above their rating for a few milliseconds. It is the same estimate the PC builder and build planner use.