All worked examples below use explicitly chosen inputs. They are not measured household averages, utility quotes, or guaranteed savings.
Start with one watt
One watt is 0.001 kW. Over 24 hours and 365 days it uses 0.001 × 24 × 365 = 8.76 kWh. This conversion gives a convenient way to check annual standby scenarios.
The main calculator’s annual result repeats the entered monthly schedule 12 times. At 30 days per month that is 360 days. Use the 365-day formula here if you specifically need a calendar-year continuous-use estimate.
Small powers, explicit annual totals
These are selected powers for illustrating the math, not measured averages for TVs, chargers, or any particular product.
| Standby power | Yearly kWh | Yearly cost, rounded |
|---|---|---|
| 1 W | 8.76 | $1.75 |
| 5 W | 43.80 | $8.76 |
| 10 W | 87.60 | $17.52 |
Subtract the hours already counted as active use
If a device operates for four hours daily and spends the other 20 hours in standby, calculate those periods separately. Using 24 hours of standby plus four hours of active use double-counts four hours.
For an illustrative device at 100 W for four hours and 5 W for 20 hours, daily energy is 0.4 + 0.1 = 0.5 kWh. At 20¢, that costs $0.10 per day.
Measure before deciding what to unplug
A charger’s output capacity is not its idle electricity consumption. Use a meter suitable for low-power readings and observe the device in the state you want to estimate. The general measurement approach is described by Virginia Cooperative Extension.
Do not turn off devices whose continuous operation you need, such as essential network, safety, medical, or preservation equipment. This page estimates the arithmetic of a chosen state; it does not decide whether interruption is appropriate.
Reference: Virginia Cooperative Extension: estimating appliance energy use
Sources & calculation notes
References checked 2026-10-09. Example arithmetic is calculated by HomeWattCheck. Article review dates are separate from the EIA data period displayed in our calculators.
Each calculator states its scope beside the result. Appliance tools estimate electricity at one rate; the time-of-use comparator includes two price periods and entered fixed fees. Complex tariffs may need additional calculations. State averages describe reported residential revenue per kWh, not your utility’s offer. See our data sources and methodology or state rate comparison.