Vampire Power Cost Calculator
Annual, monthly and daily cost of standby power from the number of devices, watts each, hours a day and your rate, with kWh and CO2. How it works
Use the Vampire Power Cost Calculator
About the Vampire Power Cost Calculator
Ten devices drawing 5 W each in standby 24 hours a day use 1.2 kWh a day and 438.30 kWh a year, which costs $52.60 a year at $0.12 per kWh. That is 4.1% of the 10,791 kWh the average US home bought in 2022 (EIA) and about 336 lb of CO2 at 0.348 kg per kWh. The $0.12 rate is only a starting value: at $0.183, close to the EIA’s US residential average of 18.31 cents for July 2026, the same load costs $80.21 a year.
Cost of constant standby power at $0.12 per kWh, 24 hours a day
| Total standby power | Energy a year | Cost a year | Cost a month | CO2 a year |
|---|---|---|---|---|
| 5 W | 43.83 kWh | $5.26 | $0.44 | 33.6 lb |
| 10 W | 87.66 kWh | $10.52 | $0.88 | 67.3 lb |
| 25 W | 219.15 kWh | $26.30 | $2.19 | 168.1 lb |
| 50 W | 438.30 kWh | $52.60 | $4.38 | 336.3 lb |
| 100 W | 876.60 kWh | $105.19 | $8.77 | 672.5 lb |
Total standby power is devices times watts each. A year is 365.25 days and a month is 30.44 days, as the calculator counts them.
10 devices at 5 W for 24 hours a day, by electricity rate
| Rate per kWh | Cost a day | Cost a month | Cost a year |
|---|---|---|---|
| $0.10 | $0.12 | $3.65 | $43.83 |
| $0.12 | $0.14 | $4.38 | $52.60 |
| $0.15 | $0.18 | $5.48 | $65.75 |
| $0.20 | $0.24 | $7.31 | $87.66 |
| $0.30 | $0.36 | $10.96 | $131.49 |
The energy is the same in every row, 438.30 kWh a year; only the rate changes.
Assumptions
- Every device draws its stated standby power for all the hours entered, with no change over the day.
- The household comparison uses the 2022 EIA average for a US residential customer, 10,791 kWh, and the CO2 uses the 2023 EPA national average.
How to use this tool
- Type the number of devices (1 to 100) and the average standby watts for each (0.1 to 100). A plug-in watt meter gives the real figure. Add another device line, up to five, for devices with different watts or hours.
- Type your electricity rate in dollars per kWh (0.01 to 1.00) and the hours a day the devices sit in standby (1 to 24, whole hours).
- Read the daily, monthly and annual cost, the annual kWh, the share of an average US household’s use and the CO2 estimate. Reset restores the example values.
Frequently asked questions
- How much does standby power cost per year?
- Multiply the total standby watts by the hours a day, by 365.25 days, divide by 1,000 and multiply by your rate. 50 W in total for 24 hours a day is 438.30 kWh, or $52.60 a year at $0.12 per kWh. A single device drawing 5 W costs $5.26 a year at the same rate.
- How do I calculate vampire power cost for one device?
- Take a cable box you measured at 20 W in standby, plugged in 24 hours a day: 20 × 24 / 1000 = 0.48 kWh a day. Times 365.25 days is 175.32 kWh a year, and at $0.12 per kWh that is $21.04. Enter 1 device, 20 W, $0.12 and 24 hours to see the same numbers.
- What percentage of home electricity is vampire power?
- A 1998 Lawrence Berkeley National Laboratory study estimated about 5% of US residential electricity and said the figure was based on estimates; a later LBNL measurement found it could reach 10% in some homes. The percentage on this page is different: it compares your annual kWh with the EIA’s 2022 average of 10,791 kWh per residential customer, which is 4.1% for the default 438.30 kWh.
- Which of my devices costs the most on standby?
- Give each device its own line with Add another device (up to five), typing its count, watts and hours, and name it if you like. The table under the result gives each line’s kWh and cost a year. 10 devices at 5 W plus 1 cable box at 20 W, all 24 hours a day at $0.12: 438.3 kWh and $52.60 for the ten, 175.3 kWh and $21.04 for the cable box, 613.62 kWh and $73.63 in total.
- How many watts does a device use on standby?
- It differs by model and age, so measure it rather than guess. Plug the device into a plug-in watt meter, switch it off with the remote or let it go idle, and read the watts. In a Berkeley Lab whole-house study (Ross and Meier, 2000) the largest standby losses came from televisions, set-top boxes and printers, so start with those. Enter the average of what you measured as the watts each.
- How is the CO2 figure worked out?
- Annual kWh times 0.348 kg of CO2 per kWh, the EPA’s eGRID2023 national average (767.209 lb per MWh), converted to pounds with 2.20462. The default 438.30 kWh gives 336.3 lb. The coal line divides that by 2.56 lb of CO2 per pound of bituminous coal (EIA), about 131 lb of coal. Your local grid may be cleaner or dirtier than the national average.
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