Standby power calculator: kWh, cost and the switched strip that cuts it

How standby power cost is worked out

The standby energy of a device is the power it draws while off, in watts, times the hours a day it sits waiting, times 365 days, divided by 1000: the result is in kWh a year. A device that draws 1 W day and night uses 8.76 kWh a year.

The calculator does this for each type of device, multiplies by how many you have and adds them up. Standby hours are 24 minus the hours of use: a TV on for 4 hours in the evening waits for the other 20. Enter the price per kWh from your bill and the cost appears; add the price of a switched extension lead (a power strip with a switch, in the US) and the calculator divides what the strips cost by the money saved each month, which gives you the months to pay them back.

The starting watts are the averages measured in English homes by the Household Electricity Survey. For microwaves and chargers, which the report does not measure on standby, the calculator uses the EU limit for new appliances. You can change all of them in the advanced options. For a device that is not on the list, use "Other devices" and enter the watts read on a plug-in energy meter. Watts and kWh are the same on 120 V and 230 V, so the numbers work in the US and the UK alike.

Worked example: living room, desk and kitchen

These are the values the calculator opens with: a TV, a set-top box, a games console and a soundbar in the living room; a PC with monitor and a printer on the desk; two chargers left plugged in; a microwave and a coffee machine in the kitchen. All on standby 20 hours a day.

• Standby power: 1.9 + 9.8 + 2.8 + 1.5 + 9.3 + 2.1 + 2 × 0.1 + 0.8 + 2.9 = 31.3 W
• Energy: 31.3 × 20 × 365 ÷ 1000 = 228 kWh a year
• The set-top box alone makes 71.5 kWh and the PC with monitor 67.9 kWh: together, more than half

At an example price of 0.30 per kWh that is 68.55 a year, 5.71 a month. Three switched leads (living room, desk, kitchen) at 10 each cost 30 and pay for themselves in 6 months, as long as you switch them off every time. Your real price per kWh is the one on your bill.

Standby power of a TV, set-top box and console

Yearly use of a single device on standby 20 hours a day:

Device	Standby	Per year
Set-top box	9.8 W	71.5 kWh
PC with monitor	9.3 W	67.9 kWh
Coffee machine	2.9 W	21.2 kWh
Games console	2.8 W	20.4 kWh
Printer	2.1 W	15.3 kWh
TV	1.9 W	13.9 kWh
Soundbar	1.5 W	11 kWh
Microwave with clock	0.8 W	5.84 kWh
New device at the EU limit	0.5 W	3.65 kWh

The rows from set-top box to soundbar are averages measured in 2010 and 2011; the last two are legal limits for new appliances. In the EU, since 9 May 2025, Regulation 2023/826 allows new appliances in its scope at most 0.50 W on standby, or 0.80 W if they show a display or a clock. Set-top boxes, consoles and other networked devices have a higher cap: up to 2.00 W in networked standby, which is 14.6 kWh a year at 20 hours a day. In the same English measurements, everything left on standby in a home added up to between 47 and 81 W.

Switched extension lead or smart plug: what to buy

You need one strip for each group of sockets close together: usually the TV unit, the desk and the kitchen worktop. Count the groups and enter the number in the strips field. Each strip needs enough sockets for every plug in its group, adapters included.

• Switched extension lead or power strip. Switched off, it cuts the devices off completely and standby drops to zero. Put it where you can reach it without bending down, or it ends up always on.
• Smart plug. It switches off on a timer or from your phone, handy for the set-top box and the console. It stays on Wi-Fi, though, and draws a little power itself: check its watts in the spec sheet before buying.
• Chargers. A new power supply with no phone attached draws at most 0.10 W: unplugging it saves little, but it can go on the same strip as everything else.

Common mistakes

• Cutting power to things that must stay on. Fridge, freezer, boiler, alarm and router do not go on a strip you switch off. Some OLED TVs need power for a while after being switched off: check the manual for how long to wait.
• Switching an inkjet printer off at the strip. Turn it off with its own button first, so it parks the print heads, then switch off the strip.
• Counting 24 hours for everything. Hours of use are not standby: with the TV on for 4 hours, standby is 20 hours.
• Trusting the starting watts. They are averages over many devices: your set-top box may draw much less or much more. A plug-in energy meter tells you, and the value goes in the advanced options.
• Buying the strip and leaving it on. It only pays back if you switch it off: the months in the calculator assume you do it every time the devices are not in use.