Hong Life CalculatorsUnderstanding the standby power cost calculator — concept and principle
Standby or "vampire" power is the electricity devices draw while they appear to be off or idle: TVs waiting for a remote signal, chargers left in the wall, routers, set-top boxes, smart speakers and appliances with clocks. Each draw is small, but it never stops. This calculator adds up your total always-on watts and shows the energy and cost over a full year.
How it is calculated
- kWh per year = W × 8,760 ÷ 1000 = W × 8.76
- Yearly cost = kWh per year × price per kWh
A year has 365 × 24 = 8,760 hours, so every watt drawn continuously becomes 8.76 kWh a year. Enter the sum of all standby loads in watts. The easiest way to get it is a plug-in energy meter on each power strip, or reading your home meter at night with everything "off".
The principle
Energy is power × time. Normal appliances run for some hours a day, but standby loads run all 8,760 hours, so a tiny wattage is multiplied by a huge number of hours. That is why 1 W may sound trivial yet still costs a couple of dollars a year at typical prices. The International Energy Agency's "One Watt" initiative and regulations such as the EU ecodesign rules pushed new devices to very low standby draw, but older equipment and networked devices that stay connected can draw much more.
Worked example
- Inputs: 25 W of total standby load, $0.25 per kWh.
- Yearly energy: 25 × 8,760 ÷ 1,000 = 219 kWh.
- Yearly cost: 219 × $0.25 = $54.75.
| Total standby watts | Yearly cost |
|---|---|
| 6.25 | $13.69 |
| 12.5 | $27.38 |
| 18.8 | $41.06 |
| 25 | $54.75 |
| 31.2 | $68.44 |
| 37.5 | $82.13 |
| 50 | $109.50 |
How to read the result
Each continuous watt costs 8.76 kWh a year, which at $0.25 per kWh is about $2.19. Use this rule to judge whether a device is worth switching off. Typical homes have a mix: chargers and modern TVs well under 1 W in standby, while older set-top boxes, game consoles in instant-on mode and some audio equipment can draw several watts or more. Switchable power strips or timers cut the biggest groups.
Common mistakes
- Counting devices that are truly off at the plug.
- Unplugging the router or alarm system that needs to stay on.
- Forgetting that the measured night-time base load also includes the fridge and other appliances that are actually working.
Frequently asked questions
How much does 1 watt of standby cost per year?
8.76 kWh; at $0.25 per kWh that is about $2.19.
Do phone chargers use power with no phone attached?
Usually a very small amount, often well below one watt for modern chargers.
Is it worth unplugging everything?
Target the largest loads first; a meter shows which devices matter.
Sources: International Energy Agency — One Watt Initiative · Commission Regulation (EC) No 1275/2008 — ecodesign requirements for standby and off mode