Add the two displays, not the whole desk twice
Measure monitor A and monitor B separately, or measure both through one suitable power strip. If the computer is connected to that strip, the result is a workstation total rather than monitor-only energy. USB-C power delivery can also move laptop charging into the monitor measurement, so state what was connected.
ENERGY STAR monitor criteria account for On and Sleep modes and vary with screen characteristics and features. For your bill, use the exact models’ documented energy or representative meter readings rather than assuming that equal screen size means equal power.
Calculate active and sleep periods
Suppose the two displays average 50 W combined for eight active hours. Active monthly energy is 0.050 × 8 × 30 = 12 kWh, costing $2.16 at $0.18/kWh. If combined sleep averages 1 W for the remaining 16 hours, that adds 0.48 kWh and about $0.09, for $2.25 total.
Do not add 24 sleep hours on top of eight active hours. The periods must total 24. If one monitor is used only occasionally, give it its own schedule rather than assigning the same active hours to both.
| Combined average | Active hours/day | 30-day active energy | Active cost at $0.18/kWh |
|---|---|---|---|
| 30 W | 8 | 7.2 kWh | $1.30 |
| 50 W | 8 | 12.0 kWh | $2.16 |
| 80 W | 10 | 24.0 kWh | $4.32 |
Test the second screen as the decision variable
Measure the primary-monitor routine, then add the second monitor under a similar workload and schedule. The difference captures the added display only if computer workload and USB charging remain comparable. A second high-resolution display can also affect computer power, which belongs in a whole-workstation test.
Record brightness, refresh mode, HDR state and sleep timing. These settings can change energy and usability, so compare comfortable configurations rather than forcing identical values that do not suit the work.
Use power management consistently
ENERGY STAR recommends activating monitor sleep settings. Verify that both displays enter sleep when the computer is inactive and that screen savers are not keeping the system awake. Recheck after software or dock changes.
The most useful monthly result separates display-only energy, computer energy and charging. That allows the user to decide whether the added screen’s productivity value justifies its measured cost without exaggerating either side.
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.