A/B Testing PC Power Supply (Annual) Calculator
Compare two PC power supplies to estimate their annual electricity use, running cost, and potential energy savings.
Overview
Use this A/B PC power supply calculator to compare the annual electricity use and cost of two PSUs. Enter your PC's typical component load, each unit's estimated efficiency, your usage pattern, and your electricity price to see the likely difference.
How it works
A power supply draws more power from the wall than it delivers to PC components because some energy is lost as heat. The calculator divides the PC component load by each PSU's efficiency to estimate wall power draw. It then multiplies that power by your annual operating hours, converts watt-hours to kWh, and applies your electricity price. A positive saving means power supply B is estimated to cost less to run than power supply A.
How to use this calculator
- 1Enter your PC's average component power load in watts.
- 2Add the estimated efficiency for power supply A and power supply B.
- 3Enter how many hours per day and days per year you use the PC.
- 4Enter your local electricity price per kWh.
- 5Review the estimated annual costs and the difference for power supply B.
Example Calculation
Average PC component load
400
Power supply A efficiency
80%
Power supply B efficiency
90%
Average use per day
5
Days used per year
365
Electricity price
0.16
Estimated annual saving with power supply B
$16.22
At a 400 W component load used for 5 hours daily, PSU A draws about 500 W from the wall while PSU B draws about 444 W. PSU B uses roughly 101.4 fewer kWh per year and saves about 16.22 in the entered currency at a rate of 0.16 per kWh.
Frequently asked questions
What does PC power supply efficiency mean?
Efficiency is the share of electricity drawn from the wall that reaches your PC components. For example, an 80% efficient PSU needs about 500 W from the wall to provide 400 W to the PC.
Does a higher-wattage power supply always use more electricity?
No. A PSU's rated wattage is its capacity, not its constant power use. Electricity use depends mainly on PC load and the PSU's efficiency at that load.
Why does power supply efficiency change with load?
PSUs are typically most efficient across part of their operating range. Efficiency can be lower at very light loads and near maximum capacity, so use figures relevant to your typical load where possible.
Does this calculator include monitor and peripheral electricity use?
No. It estimates the PC system power supplied through the PSU. Add separate electricity use for monitors, speakers, networking equipment, and other peripherals if needed.
Can I use an 80 PLUS rating as the efficiency value?
An 80 PLUS rating can provide a useful guide, but actual efficiency depends on load and testing conditions. Use a measured value or a typical efficiency figure for your expected load when available.
What does a negative annual saving mean?
A negative result means power supply B is estimated to use more electricity and cost more annually than power supply A under the values entered.
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Assumptions and warnings
Assumptions
- Both power supplies run the same PC component load for the same number of hours.
- The entered efficiency percentages represent typical efficiency at your normal operating load.
- Electricity use is calculated from wall power draw and the electricity price you enter.
- Results are estimates and do not include standby use, monitor use, or changes in component power demand.
Warnings
- This calculator provides an electricity-cost estimate only and is not financial advice.
- Actual power supply efficiency varies with load level, temperature, input voltage, age, and hardware configuration.