Define what the reading includes
A monitor may also power USB accessories or charge a laptop over a compatible connection. If you measure at the monitor’s wall plug, that energy can include more than the display panel. Do not compare such a reading with a display-only specification without explaining the difference.
Record the brightness setting, image mode and connected devices. Use a representative work session rather than a momentary reading from an unusually bright or dark screen.
Calculate active use and sleep separately
At an assumed 30 W for eight hours on 22 days, the display uses 5.28 kWh. At $0.18/kWh, that is $0.9504, rounded to about $0.95. Two identical displays on the same schedule double this active-use amount to about $1.90.
If a monitor hypothetically averages 0.5 W for another 544 hours of a 30-day month, it adds 0.272 kWh and about five cents. The active and sleep hours together equal that month’s 720 hours.
Check that sleep is working
ENERGY STAR monitor guidance covers on, sleep and off operation and recommends enabling sleep settings. Verify that the display actually enters the intended state after your timeout. A moving screen saver is still displaying an image.
If a connected device prevents sleep or keeps a charging function active, record that behavior. Changing only the computer’s screen timer may not disable every powered function in the display.
Compare comfort before replacement
Use a readable brightness and the display arrangement needed for your work. Reducing an unnecessary second screen’s active hours is a different decision from buying a new monitor. For a purchase comparison, match required size and features, apply your own schedule and include the price premium. A small monthly electricity difference rarely tells the whole story when text clarity, usable workspace and connectivity determine whether the monitor does its job.
Choose your next step
Continue with the question that matches your next decision:
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.