PSU wattage calculator
Select your parts. We take the graphics card's measured gaming power from TechPowerUp, add the CPU's power (TDP; for Intel 12th gen and later, maximum turbo power) and about 75 W for the rest of the system, and pick the smallest common PSU size that keeps that load at or under 80% of the label (70% for the few older cards without spike data) and the card's measured spikes under it — never below the card maker's or TechPowerUp's recommendation.
How it sizes the supply
We start from the graphics card's measured gaming power (TechPowerUp's review of that card), add the CPU's rated power and about 75 W for the rest of the system, and keep that sustained load at or under 80% of the label. The card's measured 20 ms spikes must also stay under the label. The safe choice never goes below the card maker's recommended PSU or TechPowerUp's minimum, whichever is higher; where the measured numbers allow it we also show a smaller size that is fine with a good-quality unit. Full rule on the methodology page.
What the estimate leaves out
Heavy overclocking, many hard drives, RGB controllers and pump-driven water cooling each add tens of watts. If your build has several of these, step up one tier.