About the Phantom Load Calculator
This phantom load calculator estimates how much electricity your devices use while they are switched off or idle but still plugged in — often called standby, vampire or idle power. List each device with its standby wattage and how many you have, and the calculator adds up the continuous load, converts it into kWh per year and shows the cost at your electricity price.
Most modern chargers and TVs draw well under a watt or two in standby, but cable and satellite boxes, game consoles left in instant-on or rest mode, desktop computers, AV receivers and older appliances can draw 5–30 W around the clock. Because standby runs almost every hour of the year, a few such devices can add up to several hundred kWh annually.
The default list uses typical standby figures; for accuracy, measure your own devices with an inexpensive plug-in watt meter while they are off. Enter the hours per day each device sits idle (the default applies to all lines unless you add a fourth value on a line), and the share of that standby you expect to eliminate with smart power strips, timers or unplugging.
With the default inputs, the yearly cost of phantom load is $59.44. Change any value above to recalculate instantly.
How to use the phantom load calculator
- 1List each device on its own line with its standby watts and quantity.
- 2Add idle hours per day as a fourth value (after the quantity) on any line that differs from the default.
- 3Enter your electricity price and monthly kWh from your bill.
- 4Set how much standby you could eliminate with smart strips or unplugging.
- 5Review the cost, the biggest offenders and the potential savings.
Formula and method
Each device’s standby wattage is multiplied by the quantity and by the hours per day it sits idle, then by 365 days and divided by 1,000 to convert watt-hours to kilowatt-hours. The device totals are summed and multiplied by your electricity price to give the yearly cost.
The share of your bill compares standby kWh with twelve months of your total use. Savings assume the percentage you enter is removed entirely, for example by smart power strips that cut power to a TV’s accessories when the TV is off. Standby wattage varies a lot between models, so measured values give the most accurate result.
- W_i
- Standby power of device i in watts
- qty_i
- Number of identical devices
- h_i
- Hours per day the device is idle but plugged in
Worked examples
Typical living room and office
The eight lines add up to 47.9 W of idle load. Over 20 hours a day for 365 days that is about 350 kWh, or $59 a year at $0.17/kWh — about 3.2% of a 900 kWh/month household’s use. The DVR alone accounts for 146 kWh.
Always-plugged-in devices at a high electricity price
If the same devices are idle around the clock and power costs $0.30/kWh, standby uses about 420 kWh and $126 a year, or $1,259 over ten years. Removing 75% of it would save about $94 a year.
Custom list with per-device hours
The set-top box and chargers use the 20-hour default, while the two coffee makers are idle 22 hours a day. Total idle draw is 28 W, about 212 kWh or $46.57 a year at $0.22/kWh, roughly 2.9% of a 600 kWh/month bill.
Frequently asked questions
How much does phantom power really cost?+
For most homes it amounts to a few percent of the electricity bill — typically $30–$150 a year depending on how many always-on devices you have and your price per kWh. Homes with several set-top boxes, game consoles and desktop computers sit at the high end.
Which devices use the most standby power?+
Cable and satellite boxes with DVRs, game consoles left in instant-on or rest mode, desktop computers, AV receivers and subwoofers, and older printers tend to be the largest. Phone chargers and modern TVs usually draw well under 1–2 W when idle.
Do chargers use electricity when nothing is plugged in?+
Yes, but very little. Modern phone and laptop chargers typically draw a fraction of a watt with no device attached, so one charger costs well under a dollar a year. Older transformer-style power bricks that feel warm when idle can draw several watts.
Do smart power strips save money?+
They can, especially in a home-theater or computer setup. An advanced strip senses when the main device such as a TV or computer turns off and cuts power to peripherals like soundbars, consoles and speakers. Savings depend on how much idle power those peripherals draw.
How do I measure standby power?+
Plug the device into a plug-in electricity usage monitor (a watt meter), switch the device off or let it go to sleep, and read the watts after a minute or two. For a device whose draw varies, leave it on the meter for a day and divide the kWh by 24 hours to get average watts.