Which power supply wattage do you need?

Updated 5 October 2026

The processor and the graphics card use most of the power in a PC. Add their power draw, add about 100 W for everything else, and choose a power supply with 30 to 40 percent to spare.

How do you work it out?

Take the processor power draw and the graphics card power draw from the maker's spec sheets. Add them. Add roughly 100 W for the motherboard, memory, drives and fans. Multiply the total by 1.3 to 1.4.

Example: a 105 W processor and a 220 W graphics card come to 325 W. With 100 W for the rest that is 425 W. A 600 W or 650 W supply covers it with room for short spikes.

Why leave headroom?

Graphics cards draw more than their rated power for a few milliseconds at a time. A supply running near its limit is also louder and less efficient. Headroom also leaves room for a later upgrade.

What do Bronze, Gold and Platinum mean?

They are efficiency ratings under the 80 Plus scheme. A Gold unit wastes less power as heat than a Bronze one at the same load. The rating is about efficiency. It does not by itself tell you how well the unit is built, so read a review of the exact model.

Which cables matter?

Check that the supply has the graphics power connectors your card needs. Many recent cards use a single 16-pin connector, and older or smaller cards use one to three 8-pin connectors.