PC Power Supply Calculator — Find Your Ideal PSU Wattage

Why does headroom matter?

PSUs are most efficient when running at 50–80% of their rated capacity. The 80 PLUS certification tests efficiency at 20%, 50%, and 100% load — most units peak at ~50% load.

Running a PSU at 90%+ load for extended periods increases heat, reduces lifespan, and can cause instability during power spikes (especially GPU boost transients). A 20% buffer protects against this.

For future-proofing: if you plan to overclock, add more drives, or upgrade your GPU within a year, sizing up one tier now is cheaper than buying a new PSU later.