Phantom power calculator
Devices you could switch off (everything except the modem and router) cost about – a year.
The default watts are average idle draws per device from NRDC’s audits of 10 California homes (2015), not a measurement of yours. Every watt drawn around the clock uses 8.76 kWh a year. The rate starts at 18¢, close to EIA’s 2026 U.S. average; change it to the rate on your bill.
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How to use it
- Set how many of each device you have. Set a row to 0 if you do not have it.
- Replace the watts with your own readings if you can. Plug the device into an electricity usage monitor, switch it off as you normally would and read the watts.
- Enter your rate: divide the total on your electric bill by the kWh used that month.
Where the default numbers come from
NRDC measured the always-on power of individual devices in 10 homes around San Francisco and reported the average idle draw for each type: set-top boxes about 16 W, TVs 13 W, modems 11 W, desktop computers 9.5 W, audio and video devices 7.5 W, laptops 7.1 W, printers 6.3 W and wireless routers 5.5 W (NRDC, Home Idle Load, 2015). The same report measured an Xbox One with “instant on” at 12 W and found a TV’s quick-start setting drawing up to 37 W around the clock.
NRDC says the sample is not statistically representative, and newer devices are often more efficient. Treat the defaults as a starting point and measure the big ones.
For scale: across its larger sample, NRDC found the average home’s always-on load was about 164 W, nearly 23% of household electricity use. That figure includes things this calculator leaves out, such as hot water recirculation pumps, security systems and lights left on.
What one watt costs
| Always-on draw | kWh per year | Cost per year at 18¢ |
|---|---|---|
| 1 watt | 8.8 | $1.58 |
| 10 watts | 87.6 | $15.77 |
| 25 watts | 219 | $39.42 |
| 50 watts | 438 | $78.84 |
| 100 watts | 876 | $157.68 |
Measure the big ones
A plug-in meter shows what a device really draws when it is “off”. The P3 Kill A Watt EZ P4460 also shows the cost per week, month and year once you enter your rate; its screen is not backlit, which makes readings behind a TV stand awkward.
To switch an entertainment center off on a schedule, an energy-monitoring smart plug like the Tapo P115 (2-pack) logs usage in an app and can cut power overnight. It needs an account and 2.4 GHz Wi-Fi, and it is not for space heaters. We compare more meters in the best electricity usage monitors.
How to cut it
- Change settings first: turn off TV quick-start and switch consoles from instant-on to energy-saving mode.
- Switch groups off together with a switched power strip or a scheduled smart plug. Keep a recording DVR, the modem and the router on a separate outlet.
- Unplug what you rarely use: the guest-room TV, the spare printer, the old stereo.
More detail, and what to leave alone, in our guide to phantom power.
FAQ
How much does phantom power cost a year?
Every watt a device draws around the clock costs about $1.58 a year at 18 cents per kWh. A typical entertainment center, laptop charger, printer and network gear can add up to 70–80 W, or roughly $110–$125 a year. NRDC found the average home’s total always-on load was about 164 W.
Which devices use the most standby power?
Cable and satellite boxes, TVs with quick-start, game consoles in instant-on mode, desktop computers and audio equipment are usually the biggest. Phone chargers with nothing attached usually draw well under a watt.
Is it worth unplugging things to save electricity?
For the big always-on devices, yes: changing settings or using a switched power strip captures most of the saving with no effort. Unplugging small chargers saves very little.
Email me at hello@thelowbillhome.com. I read every message, and when a rate, a rule or a product changes, I update the guide. — Eugene
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