A/B Testing PC Power Supply (Per-User) Calculator
Compare estimated power supply requirements for two PC configurations and check how much headroom each setup has on a selected PSU.
Overview
Use this A/B PC power supply calculator to compare the estimated PSU requirement for two individual PC configurations. Enter peak CPU, GPU, and other component power for each build, choose a headroom margin, and check the load on a PSU you are considering.
How it works
The calculator adds the CPU, GPU, and other component estimates for each configuration to estimate peak component demand. It then adds your chosen percentage of headroom and rounds the result up to the next 50 W PSU size. The selected PSU load shows estimated component demand as a percentage of that PSU’s rated continuous output. PSU efficiency affects power drawn from the wall, but it does not reduce the PSU’s rated DC output capacity used in this comparison.
How to use this calculator
- 1Enter the expected peak CPU, GPU, and other component power for Configuration A.
- 2Enter the same power estimates for Configuration B.
- 3Choose the extra PSU headroom you want to keep available.
- 4Enter the rated wattage of the PSU you want to compare.
- 5Review each recommended PSU size and the estimated load on the selected PSU.
Example Calculation
Configuration A CPU power
125
Configuration A GPU power
320
Configuration A other components
100
Configuration B CPU power
65
Configuration B GPU power
220
Configuration B other components
90
Desired power headroom
30%
PSU wattage to check
750
Recommended PSU for Configuration A
750 W
Configuration A has an estimated component demand of 545 W and rounds to a 750 W recommendation with 30% headroom. Configuration B has an estimated demand of 375 W and rounds to a 500 W recommendation. On a 750 W PSU, their estimated component loads are about 72.7% and 50.0% respectively.
Frequently asked questions
What power figures should I enter for my CPU and GPU?
Use realistic peak or sustained load figures from reliable product specifications or detailed reviews. For CPUs, the base power rating may be lower than actual boost power.
How much PSU headroom should I choose?
A margin of around 20% to 30% is a common starting point for many systems. More may be useful for high-power GPUs, overclocking, future upgrades, or uncertain component estimates.
Does a higher-wattage PSU always use more electricity?
No. A PSU supplies the power the PC demands; its wattage rating is its maximum rated output capacity. Actual wall use also depends on PSU efficiency and system load.
Why does the calculator round up to 50 W?
PSUs are commonly sold in capacity steps such as 550 W, 650 W, 750 W, and 850 W. Rounding up avoids suggesting a capacity below the calculated requirement.
Can I use this calculator for multiple users or workstations?
The results apply to one PC at a time. For multiple separate workstations, calculate each PC individually because each needs its own appropriately sized PSU.
Does wattage alone confirm that a PSU is suitable?
No. Also check PCIe and CPU power connectors, physical size, power supply quality, protections, and compatibility with the specific graphics card and motherboard.
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Assumptions and warnings
Assumptions
- Component power entries represent realistic peak DC power demand rather than idle or base-power figures.
- The selected headroom is intended to allow for sustained load, normal aging, upgrades, and brief power spikes.
- Recommendations are rounded up to the next 50 W capacity, a common PSU size increment.
- The calculation considers rated wattage only; it does not assess connector availability, rail design, PSU quality, or physical fit.
- Results are per PC user or workstation and should not be multiplied across users unless each user has a separate PSU.
Warnings
- This calculator provides an estimate only and is not electrical or purchasing advice.
- Check that the PSU has the required GPU, CPU, and storage connectors and is from a reputable manufacturer.
- High-end GPUs can have short transient spikes that may require more headroom than a basic wattage estimate suggests.