PSU Wattage Calculator
| Build class | CPU + GPU draw | Est. peak | Recommended PSU |
|---|---|---|---|
| Office, iGPU | 65 + 0 | ~155 W | 450 W |
| Mainstream gaming | 125 + 220 | ~445 W | 650 W |
| Performance | 170 + 320 | ~590 W | 850 W |
| Flagship | 170 + 450 | ~720 W | 1000 W |
Enter your processor and graphics card power draws plus a rough estimate for everything else in the case. The calculator totals a realistic peak, adds headroom for the millisecond spikes that trip undersized units, and rounds up to the next power supply you would actually buy.
The sizing rule that matters is load percentage: a power supply runs its best efficiency curve, quietest fan and longest life between half and sixty percent of its rating. That is why the right answer is rarely the peak number - a 500 watt system wants a 750-850 watt unit, not a 550 watt one living at its ceiling.
How to use
- CPU draw is the TDP or PBP off the spec sheet - 65 for office chips, 125 to 250 for unlocked desktop parts.
- GPU draw is the board power, not the power connector math: 165 for mid-range, 220 to 320 for performance class, 450 for the flagship tier.
- Count the rest honestly - drives, fans, AIO pump, RGB - typically 30 to 60 watts. The verdict updates live and rounds to standard unit sizes.
Frequently asked questions
What power supply do I need for a gaming PC?
Add CPU and GPU draw plus about 75 watts of platform, then nearly double it: a 125 watt chip with a 220 watt card peaks near 420 and lands on a 650-750 watt unit running at a comfortable half load. The calculator does the sum and rounds to shelf sizes.
Why does my PSU need headroom above the peak number?
Transients: modern graphics cards spike to double their rated board power for microseconds on load changes, and an undersized unit shuts down as protection - the infamous black-screen-under-load. Headroom is not wasted watts, it is the shock absorber for those spikes.
Is 50 percent load really the sweet spot?
Yes, for three compounding reasons: the efficiency curve peaks near half load, the fan often does not even spin there, and the capacitors age slowest when cool. A unit loafing at 50-60 percent is quieter today and still healthy in eight years.
What do 80 Plus ratings actually mean?
Efficiency only, not quality: Bronze, Gold and Platinum describe how much wall power becomes DC heat at test loads. A Gold unit wastes less and runs cooler than Bronze, but says nothing about capacitors, protection circuits or the transient behavior that actually kills systems.
Do I need ATX 3.0 for a new graphics card?
It is the first spec written for GPU transients rather than steady draw, so for flagship cards it is cheap insurance - and the native 12VHPWR cable beats an adapter for one less connection to fail. For mid-range builds a quality older-spec unit with headroom still serves fine.