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 average — TechPowerUp measured the RX 6900 XT at 305 W while gaming but 636 W in its highest 20 ms spike. 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
Sustained load = the graphics card's measured average gaming power (from TechPowerUp's testing of that card) + CPU power (TDP, or maximum turbo power for Intel 12th gen and later; games usually draw less) + 75 W for the motherboard, memory, storage and fans. A size fits when that load is at most 80% of the label and the card's measured spike plus the rest of the system stays under the label (70% when the review has no spike data). The table shows the safe choice: the smallest size that fits and also meets the higher of the card maker's recommended PSU and TechPowerUp's minimum. Each card's own page also shows a smaller "good unit" size where the measured numbers allow it.
| Graphics card | CPU | Sustained load | Safe PSU |
|---|---|---|---|
| RTX 5090 | Core i3-13100F | 772 W | 1000 W |
| RTX 5090 | Core i5-14600K | 843 W | 1200 W |
| RTX 5090 | Ryzen 7 9800X3D | 782 W | 1000 W |
| RX 7900 XT | Core i3-13100F | 505 W | 750 W |
| RX 7900 XT | Core i5-14600K | 576 W | 750 W |
| RX 7900 XT | Ryzen 7 9800X3D | 515 W | 750 W |
| RTX 3090 | Core i3-13100F | 553 W | 850 W |
| RTX 3090 | Core i5-14600K | 624 W | 850 W |
| RTX 3090 | Ryzen 7 9800X3D | 563 W | 850 W |
| RX 6800 | Core i3-13100F | 420 W | 650 W |
| RX 6800 | Core i5-14600K | 491 W | 650 W |
| RX 6800 | Ryzen 7 9800X3D | 430 W | 650 W |
| RTX 2080 Ti | Core i3-13100F | 457 W | 650 W |
| RTX 2080 Ti | Core i5-14600K | 528 W | 750 W |
| RTX 2080 Ti | Ryzen 7 9800X3D | 467 W | 650 W |
| RX 6650 XT | Core i3-13100F | 374 W | 550 W |
| RX 6650 XT | Core i5-14600K | 445 W | 650 W |
| RX 6650 XT | Ryzen 7 9800X3D | 384 W | 550 W |
| GTX 1650 | Core i3-13100F | 249 W | 450 W |
| GTX 1650 | Core i5-14600K | 320 W | 550 W |
| GTX 1650 | Ryzen 7 9800X3D | 259 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: a native 12V-2x6 cable avoids adapters.
- 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.