PSU calculator

How the calculator works

A power supply has to cover the worst moment, not the average one. We add the rated power of your graphics card, the power of your processor and 100 W for the motherboard, memory, drives and fans. We then add 15 percent headroom for a minimum and 40 percent for a comfortable size, and round up to the next common power supply size.

High-end Intel processors draw far more than their rated power when they boost, so we count 1.7 times the rated figure for Intel chips rated 100 W or more, and 1.2 times for the rest. That matches what people measure in games and in short bursts.

Choosing a power supply

Pick the recommended size if you can. A power supply that runs at 50 to 60 percent of its rating is quieter, cooler and more efficient, and it leaves room for a stronger graphics card later. Buy from a known brand, look for an 80 Plus Gold rating or better, and check that it has the right power connectors for your card. Current high-end cards use a 12V-2x6 connector, or two or three 8-pin connectors.

The calculator is an estimate from rated power, not from a measurement of your build. If you overclock, run many drives or use several fans and extras such as RGB and capture cards, move up one size.

Common mistakes

The usual error is to size a supply by the graphics card alone. The processor matters too, especially a high-end Intel chip, which can add 150 W or more when it boosts. The second is to buy by connector count and ignore the rating, or to reuse an old supply with a new card. Capacity falls with age, and an old 600 W unit may no longer deliver 600 W. The third is to buy a supply far larger than needed. A supply at 20 percent load is less efficient, though it is still safe.