Electricity cost calculator
See what a router, NAS, computer, or other device costs to run. Use your measured average watts and the electricity rate from your bill.
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What the result includes
This is an energy-use estimate at a constant rate. It assumes the device draws your entered average power for the same number of hours every day. A month is one-twelfth of a 365-day year. Fixed account charges, time-of-use changes, and demand charges are outside the calculation.
The formula
Daily kWh = watts × hours per day ÷ 1,000
Annual cost = daily kWh × price per kWh × 365
A worked example
A hypothetical device averaging 40 W around the clock uses 0.96 kWh a day. At an illustrative $0.20/kWh, that is $0.192 a day, $5.84 per average month, and $70.08 a year. These are example inputs, not a claim about a specific product or the rate where you live.
Where do I find the watts?
Use a suitable plug-in electricity meter for a compatible plug-in device, or reliable measured data for your exact equipment and workload. A 300 W power supply rating does not mean a computer continually consumes 300 W. Equipment that sleeps, cycles, or changes workload needs a representative average.
Which electricity price should I enter?
Enter the variable cost per kWh that changes with usage, including applicable per-kWh charges. Enter 0.20 for 20 cents, not 20. If rates change through the day, calculate each rate period separately. The currency selector changes the label; it does not fetch or convert prices.
Is switching it off worthwhile?
The cost result is one input to that decision. A router, recording device, or backup system may provide a service while nobody is actively using it. Consider what stops working before reducing its operating hours. For a purchase decision, use the upgrade payback calculator.
Read: the cost of an always-on device
Source and method
The watts-to-kWh method follows the US Energy Information Administration’s guide to measuring electricity. Examples are calculated for this tool. Methods and corrections.