The useful answerAdd the average draw of equipment used at the same time, then apply your working hours and tariff. A power supply’s maximum rating is not a measurement of ordinary office use.

Draw the boundary around your desk

List the computer, separate monitors, speakers, desk lighting and other equipment used for work. Decide whether your estimate covers only that desk or also heating and cooling the room. Keeping those categories separate makes the result easier to improve.

A power supply marked 500 W does not establish that the computer uses 500 W throughout the working day. The Department of Energy’s measurement guidance supports using energy over a period to find average power when consumption varies. Choose a representative workload rather than an unusually demanding demonstration.

Add equipment with matching schedules

For an invented office, assume the computer averages 90 W, a separate display 35 W and other desk equipment 10 W. Together they average 135 W. Eight hours per day on 22 workdays at $0.18/kWh gives:

0.135 kW × 8 × 22 = 23.76 kWh
23.76 × $0.18 = $4.2768 ≈ $4.28

If a power meter measures the complete desk setup, do not then add its individually connected devices again. If a router runs all day, give it a separate schedule rather than including it only in the eight working hours.

Account for idle periods

ENERGY STAR recommends power-management settings and notes that a screen saver is not equivalent to energy-saving sleep. Check whether the device actually enters the selected low-power mode; an application or peripheral can affect the result.

For example, an additional hypothetical 15 W idle load left on for 16 hours daily over 30 days uses 7.2 kWh and costs $1.30. That amount is separate from the workday example. Whether you can remove it depends on required background tasks and how the system is used.

Choose the most useful improvement

Record energy use alongside whether the setup completes your work comfortably. A lower-power computer that cannot handle the workload is not an equivalent alternative. Changing monitor settings or sleep behavior may be more proportionate than replacing working equipment solely for a small projected saving.

After adjusting one setting, repeat a comparable work period and note any differences in tasks. Use the running cost calculator for each schedule. If keeping the room comfortable adds significant consumption, put that in its own line so you can see whether the larger opportunity is at the desk or in the room.

Choose your next step

Continue with the question that matches your next decision:

Shopping options for this guide

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P3 P4400 Kill A Watt electricity usage meter

The P4400 displays watts and accumulates kWh. Use the energy reading with your electricity rate to estimate the cost of compatible plug-in equipment.

Before buying: For compatible North American outlets: 115 V operating voltage, 125 V maximum and 15 A maximum. Not for 230 V outlets or hardwired appliances. Check low-power accuracy before relying on tiny standby readings; record totals before unplugging, which resets the counters.

View P3 P4400 Kill A Watt electricity usage meter at Amazon.com (opens in a new tab)

These are shopping options, not hands-on test results. Check the retailer for current specifications, price and availability.

Sources & further reading

Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.