A/B Testing PC Power Supply Calculator
Compare the estimated power needs of two PC builds to see which power supply capacity provides suitable operating headroom.
Overview
Use this A/B Testing PC Power Supply Calculator to compare two PC component configurations against one PSU. Enter estimated CPU, GPU, and other component power for each build, then add a reserve for short power spikes and choose the maximum PSU loading you are comfortable with.
How it works
The calculator adds the CPU, GPU, and other component estimates for each build. It then increases each total by the transient power reserve. Each reserved total is divided by your target maximum PSU load to estimate a suitable PSU rating, and the larger of the two recommendations is shown. It also compares each reserved load with your current PSU rating, so you can see which configuration is more demanding.
How to use this calculator
- 1Enter your power supply's continuous wattage rating.
- 2Add the expected high-load CPU, GPU, and other component wattage for Build A.
- 3Enter the same estimates for Build B.
- 4Set a transient reserve to allow for short power spikes.
- 5Choose your preferred maximum PSU load and compare the results.
Example Calculation
Current PSU rated power
750
Build A CPU power
125
Build A GPU power
320
Build A other components
80
Build B CPU power
125
Build B GPU power
450
Build B other components
85
Transient power reserve
20%
Target maximum PSU load
80%
Recommended PSU rating
990 W
Build A has an estimated reserved peak load of 630 W, while Build B reaches 792 W. A 750 W PSU is estimated to run at 84.0% for Build A and 105.6% for Build B; the calculator recommends about 990 W to keep either build at or below an 80% target load.
Frequently asked questions
What wattage should I enter for my CPU and GPU?
Use realistic high-load power estimates, such as sustained package power for the CPU and expected board power for the GPU. Manufacturer specifications and reputable measured reviews can help.
Why does the calculator add a transient power reserve?
Some components, particularly GPUs, can draw brief power spikes above a typical sustained load. A reserve gives the PSU capacity margin for these events.
Is a PSU unsafe when the result is above 100%?
A result above 100% means the reserved estimate exceeds the PSU's rated continuous capacity. It is a sign to reassess the power estimates and consider a higher-capacity, suitable PSU.
Is an 80% target load required?
No. It is a commonly used planning target that leaves headroom, but the appropriate target depends on the PSU model, expected workloads, noise preferences, and upgrade plans.
Does this calculator account for PSU efficiency?
No. It compares DC component demand with the PSU's rated DC output. Efficiency affects the power drawn from the wall, not the basic output-capacity comparison.
Can I use this calculator for overclocked PCs?
Yes, provided you enter power estimates that reflect the overclocked CPU and GPU behavior. Overclocking can increase both sustained draw and short spikes.
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Assumptions and warnings
Assumptions
- Component wattage entries represent realistic simultaneous high-load usage rather than idle power.
- The transient reserve is a planning allowance for short power spikes and is not a measured peak value.
- The PSU's stated wattage is assumed to be its available continuous output capacity.
- The calculation does not assess PSU quality, connector availability, rail limits, physical fit, or efficiency certification.
- Results are estimates; actual draw varies with workload, settings, component samples, and attached devices.
Warnings
- This calculator provides an estimate only and is not electrical or purchasing advice.
- Check that the PSU has the correct GPU, CPU, and motherboard connectors before installing hardware.
- A PSU that meets a wattage estimate may still be unsuitable if it is low quality, damaged, or lacks required protections.