Guide / Running costs
The quiet cost of an always-on device
A small power draw becomes a larger number when it runs for 8,760 hours a year. Measure the draw, then decide whether changing it is worthwhile.
Start with the electricity cost calculator if you already know your average watts and rate.
One watt, one year
A continuous 1 W load uses 8.76 kWh in a 365-day year. Multiply that by your variable electricity rate. At an illustrative $0.20/kWh, each always-on watt costs $1.752/year. A 10 W reduction would save $17.52/year under those assumptions.
| Average draw | Annual energy | Annual cost |
|---|---|---|
| 5 W | 43.8 kWh | $8.76 |
| 15 W | 131.4 kWh | $26.28 |
| 40 W | 350.4 kWh | $70.08 |
| 100 W | 876 kWh | $175.20 |
These are arithmetic examples, not typical consumption claims for named devices. Two products with the same purpose can draw different amounts, and the same product can vary with workload.
Measure at the right boundary
For a compatible plug-in device, a suitable electricity meter can measure energy across a representative period. If it reports 0.96 kWh over 24 hours, the average power is 0.96 × 1,000 ÷ 24 = 40 W. Include external disks and adapters if they are part of the setup you are evaluating.
A quick reading while the machine is idle can miss work later in the day. A daily backup, disk activity, or a different sleep schedule can change the average. Record the duration and what the equipment was doing alongside the number.
Find changes that do not require a purchase
List what the device needs to do and when. A machine needed only for an evening task is a different case from a router serving an occupied home or a storage system receiving backups overnight. Test any schedule change against those requirements before assuming that all idle time is unnecessary.
Then ask whether replacement makes sense
Saving $17.52/year does not repay a $100 purchase quickly. At a constant rate and usage, simple payback is about 5.71 years. Compare the expected useful life and any extra equipment required. The upgrade payback calculator makes those assumptions visible.
Source and checking
The conversion from power and time to energy follows the US Energy Information Administration’s explanation of power and energy. Table values were calculated using the stated rate and 365 days. No hardware was tested for this guide. How these guides are produced.