This calculator adds up the hidden cost of devices left on standby. You tick the appliances that stay plugged in and idle in your home, enter your tariff, and it returns the total annual standby energy, its cost and CO2e, and points out the single worst offender to switch off first.
How it works
Standby power is drawn continuously, so each device’s yearly energy is its watts multiplied by all 8,760 hours in a year. Summing across devices and converting gives the totals:
kWh_device = standby_watts / 1000 × 8760
total_kWh = Σ kWh_device
cost = total_kWh × tariff_per_kWh
co2 = total_kWh × grid_factor (≈0.21 kgCO2e/kWh)Because the draw runs every hour of the year, even a device pulling just a few watts on standby quietly consumes tens of kilowatt-hours annually.
Why standby energy is easy to overlook
The problem is invisibility. A device that pulls 5 W on standby is doing nothing you can see — no light, no fan, no heat you notice — yet over a year it burns about 44 kWh. At a typical UK tariff that is around £11 per device, and most homes have a dozen or more devices left on indefinitely.
Unlike heating or cooling, standby power is almost entirely wasted: none of it goes toward a useful outcome. It just keeps a chip warm, a clock ticking, or a remote receiver listening.
Worked example
A living room and home office with a TV (2 W), set-top box (8 W), games console in rest mode (1.5 W), broadband router (7 W, which you may want to leave on), and a printer (3 W) consumes roughly:
| Device | Standby W | Annual kWh |
|---|---|---|
| TV | 2 | 17.5 |
| Set-top box | 8 | 70.1 |
| Games console | 1.5 | 13.1 |
| Router | 7 | 61.3 |
| Printer | 3 | 26.3 |
| Total | 21.5 | 188 kWh |
At a 24p/kWh tariff that totals around £45 per year and roughly 40 kg of CO2 (illustrative). Switch off the set-top box and console overnight — both are the biggest non-essential draws — and you cut the controllable waste by more than half.
What to do with the result
The calculator highlights the single worst offender to help you prioritise. Start there. Practical steps ranked by impact:
- A switched power strip for the entertainment cluster — one button powers everything down.
- Enable the deepest sleep mode on games consoles; manufacturers vary in how much energy rest mode uses depending on firmware settings.
- Unplug phone and laptop chargers when not actively charging; modern chargers draw less than older designs, but a room full of them still adds up.
- The router is often a deliberate choice to leave on for smart home devices or overnight downloads — the tool includes it so you can see its cost and decide.
Over a few years, the savings from switching off a handful of devices can be meaningful; the CO2 benefit compounds too as the grid decarbonises and each saved kWh avoids emissions.