How to Estimate PC Power Use and Choose a PSU

CPU and GPU ratings describe different things

AMD default TDP, Intel Maximum Turbo Power and graphics-card board power are not interchangeable measurements. A CPU’s default TDP is not its maximum electrical draw, and adding the catalog ratings will not tell you what a wall meter would show.

Keep the rating’s name beside its number. That makes it possible to understand the estimate when you change a CPU or compare two builds.

Start with the card’s recommendation, then check the supply

Find the PSU recommendation for the exact graphics-card model. Use it as a starting point, then account for your processor and the rest of the system. Before choosing a supply, check its output capacity, CPU and GPU connector counts, form factor and space for the cables inside the case.

A supply that meets the wattage recommendation still needs the right connections. Follow the PSU and GPU instructions for how those cables should be installed.

How RigAtlas calculates its estimate

The builder adds the catalog CPU power rating, the selected graphics card’s board power and a 75 W allowance for the rest of the PC. It then rounds up to the next 10 W. For a supported integrated-graphics build without a separate card, it uses the CPU rating plus the allowance.

With hypothetical ratings of 65 W for the CPU and 200 W for the card, the calculation is 65 + 200 + 75 = 340 W. This explains the displayed planning estimate; it does not recommend buying a 340 W power supply.

When the estimate leaves work to do

The fixed allowance does not itemize every drive, fan or pump. Boost settings and short power excursions also need attention when sizing a supply. If a required catalog rating is missing, RigAtlas leaves the estimate unavailable instead of supplying a guessed number.

Open Compatibility & power to see the basis. For a system with extra drives or cooling equipment, list those loads separately and check the PSU manufacturer’s guidance alongside the GPU recommendation.

Change the PSU and its cables together

Do not leave old modular cables installed just because their plugs fit the replacement supply. The PSU-side pinout can differ, including between models from the same brand. Use the new supply’s cables or ones explicitly approved for that exact model.

CORSAIR’s compatibility table is an example of the model-specific check required. If you cannot establish approval for a cable, replace it with the correct cable set rather than trying it to see whether the PC starts.

Your checklist

• Find the exact graphics-card maker’s system power recommendation.
• Check PSU output, form factor and enclosure clearance.
• Confirm CPU and GPU connector types and counts.
• Use the supplied or explicitly approved modular cable set.
• Review extra drives, fans, cooling equipment and unresolved power checks.