How much power supply headroom you actually need
A power supply has one job: deliver clean power at every load the system can produce, for years. The wattage on the box is a ceiling, not an operating point. Three things decide how far below that ceiling you should sit.
1. Efficiency has a sweet spot
Most units are most efficient between roughly 40% and 70% of their rating and run cooler and quieter there. A system that draws 500 W on a 550 W unit works, but the fan will spin up under every game and the unit will age faster. On an 850 W unit the same system idles the fan most of the time.
2. Modern graphics cards spike
High-end cards draw short bursts well above their rated board power — for a few milliseconds, sometimes 1.5–2× the label. A supply with little margin can trip its over-current protection and shut the system off mid-game. This is the reason the recommended wattage for a flagship card is higher than "CPU plus GPU plus a bit".
3. You will upgrade the card before the PSU
A good unit lasts two or three GPU generations. Buying a size up today usually costs less than replacing the supply with the next card.
How the calculator estimates it
Estimated load = CPU maximum turbo power + GPU board power + 100 W for the motherboard, memory, storage and fans. Recommended supply = the first common size at or above 1.3× that load. The 1.3 factor is where the three points above meet: it keeps typical gaming load near 60–70% of the rating and leaves room for spikes. It is deliberately conservative for small systems — a 450 W unit is fine for an office PC even if the table says 550 W for a low-end gaming pair.
| Graphics card | CPU | Estimated load | Recommended PSU |
|---|---|---|---|
| RTX 5090 | Core i3-13100F | 764 W | 1000 W |
| RTX 5090 | Core i5-14600K | 856 W | 1200 W |
| RTX 5090 | Ryzen 7 9800X3D | 795 W | 1200 W |
| RX 7900 XT | Core i3-13100F | 504 W | 750 W |
| RX 7900 XT | Core i5-14600K | 596 W | 850 W |
| RX 7900 XT | Ryzen 7 9800X3D | 535 W | 750 W |
| RTX 3090 | Core i3-13100F | 539 W | 750 W |
| RTX 3090 | Core i5-14600K | 631 W | 850 W |
| RTX 3090 | Ryzen 7 9800X3D | 570 W | 750 W |
| RX 6800 | Core i3-13100F | 439 W | 650 W |
| RX 6800 | Core i5-14600K | 531 W | 750 W |
| RX 6800 | Ryzen 7 9800X3D | 470 W | 650 W |
| RTX 2080 Ti | Core i3-13100F | 439 W | 650 W |
| RTX 2080 Ti | Core i5-14600K | 531 W | 750 W |
| RTX 2080 Ti | Ryzen 7 9800X3D | 470 W | 650 W |
| RX 6650 XT | Core i3-13100F | 369 W | 550 W |
| RX 6650 XT | Core i5-14600K | 461 W | 650 W |
| RX 6650 XT | Ryzen 7 9800X3D | 400 W | 550 W |
| GTX 1650 | Core i3-13100F | 264 W | 450 W |
| GTX 1650 | Core i5-14600K | 356 W | 550 W |
| GTX 1650 | Ryzen 7 9800X3D | 295 W | 450 W |
Things the wattage does not tell you
- Rating tier (80 Plus Bronze/Gold/Platinum) is about efficiency, not quality. A Gold unit from a weak platform is worse than a Bronze unit from a good one. Look for independent reviews of the specific model.
- ATX 3.x / 12V-2x6 matters if the card uses the 16-pin connector: native support avoids adapters and is designed for the spikes above.
- Cables: count the PCIe connectors you need. A 750 W unit with two 8-pin cables cannot power a card that wants three.
Estimate the load for your exact pair, or see the methodology for the constants.