How to Choose the Right PSU Wattage

Updated 2026-10-04

Buying too small a power supply causes shutdowns and instability. Buying far too large wastes money. A short calculation gets you to the right size.

Step 1: estimate peak load

The CPU and graphics card draw most of the power. Add them to a base of about 90 W for the motherboard, memory, drives and fans. The PSU Wattage Calculator does this and lists each part.

Step 2: add headroom

Choose a unit about 30% above your estimated peak. Short power spikes from graphics cards can exceed their rated draw, and a PSU loses some capacity as it ages.

Step 3: check connectors

Look at the graphics card's power inputs. High power cards use a 12V-2x6 connector or several 8-pin PCIe plugs. Confirm the PSU has those cables. Do not mix cables between different PSU models.

What 80 PLUS means

The rating describes efficiency at set loads. Gold is more efficient than Bronze, so it wastes less power as heat. It does not guarantee build quality. Read independent reviews and check the warranty length.

ATX 3.x

Newer units follow ATX 3.0 or 3.1, which are designed for the power spikes of modern graphics cards. They are worth considering with high power cards.