BuildPC

PSU Calculator

Total component load plus headroom — PSUs run most efficiently well under their max rating, not maxed out.

Total component wattage (W)

Safety headroom (%)

Recommended PSU (W)

455

Add up your GPU, CPU, and other components' rated wattage first — PSUs run most efficiently at 50-80% load, not maxed out.

What you entered

Total component wattage (W): 350Safety headroom (%): 30

1
Add 30% headroom for efficiency and future upgrades
350 × 1.30= 455 W

Result

Recommended PSU (W): 455

350W of components with 30% headroom calls for at least a 455W power supply.

Power supply size by component draw

Add up the sustained draw of every component, then add headroom. 30% is the usual recommendation: it keeps the unit in its efficient band and leaves room for transient spikes.

Component draw	Headroom	Recommended PSU
300 W	30%	390 W
450 W	30%	585 W
600 W	20%	720 W
600 W	30%	780 W
600 W	50%	900 W
750 W	30%	975 W

Round up to the next commercially available size. Modern GPUs draw brief spikes well above their rated power, which is why headroom matters more than the average figure suggests.

Why headroom matters

PSUs are most efficient (and quietest, and longest-lived) running at 50-80% of their rated capacity, not pegged at 100% — headroom also leaves room for future upgrades like a more powerful GPU.

GPU is usually the biggest factor

A modern high-end GPU alone can draw 300-450W under load — check your specific GPU and CPU's rated power draw (TDP) rather than guessing, since they vary enormously across different models.

Frequently asked questions

My PC build has a 350W GPU and a 125W CPU — what PSU do I need?

With about 475W of just GPU and CPU draw, plus 50-100W for the rest (motherboard, RAM, drives, fans), your total load is around 550-575W. A 750W PSU gives comfortable headroom at 75% load, where efficiency is best.

Can I use a PSU that's exactly my total wattage?

Technically yes, but it's a bad idea. A PSU running at 100% capacity generates maximum heat, runs its fan loudest, and wears out fastest. The sweet spot is 50-80% of rated capacity — size up accordingly.

Does a higher-wattage PSU use more electricity?

No. A PSU only draws as much power as the components demand. An 850W PSU running a 400W load draws about the same from the wall as a 550W PSU running that same 400W load, assuming similar efficiency ratings.

What do the 80 Plus ratings (Bronze, Gold, Platinum) mean?

They certify minimum power conversion efficiency. Gold means at least 87% efficient at 50% load — so an 87W wall draw delivers 76W to your components and wastes 11W as heat. Higher ratings waste less electricity and run cooler.