How the calculation works
Electricity is billed in kilowatt-hours, which is simply power multiplied by time. A 1,500 W appliance running one hour consumes 1.5 kWh.
The figure people underestimate is not the wattage but the hours. A 5 W standby light costs almost nothing per hour yet runs 8,760 hours a year; a 2,000 W heater costs a great deal per hour but may run only in winter evenings. Multiply before judging.
Worked example
A 1,500 W appliance used two hours a day at 0.18 per kWh:
Set against that, a 9 W LED bulb burning five hours a day costs roughly 3 a year. This is why energy advice concentrates on heating, cooling, refrigeration and hot water rather than on turning off lights.
Where the bill actually comes from
In most homes, four categories account for the large majority of consumption: space heating and cooling, water heating, refrigeration, and laundry or dishwashing. Everything else, including all electronics, usually shares a small remainder. Reducing a bill therefore starts with identifying which of those four you can shift, shorten or replace.
Off-grid, the same logic is even sharper: the heat loads that dominate a grid bill are usually excluded entirely from an off-grid system and served with propane or wood, because supplying them with panels and batteries would cost several times more than the rest of the system combined.
Common mistakes
- Treating nameplate watts as continuous. Fridges, freezers, pumps and air conditioners cycle. Use effective run hours, not hours plugged in.
- Ignoring standby loads. Individually trivial, collectively often 5 to 10% of a household bill.
- Comparing appliances by wattage alone. An efficient appliance that runs longer can cost more than a powerful one that finishes quickly. Compare kWh per task, not watts.
- Forgetting tariff structure. Where time of use pricing exists, the same kWh can cost twice as much at peak. Shifting laundry and dishwashing off peak is free money.
Frequently asked questions
How much does it cost to run a fridge?
A modern full-size fridge consumes roughly 1 to 1.5 kWh per day, so about 0.20 per day or 70 a year at 0.18 per kWh. Older units can easily use double that, which is why replacing a very old fridge often pays for itself faster than most efficiency measures.
Does turning things off at the wall really help?
Modestly. Standby draw across a typical home is a few tens of watts, worth perhaps 30 to 60 a year. Worth doing where convenient, but it is not where the bill is decided.
How do I measure an appliance rather than guess?
A plug-in energy meter costs very little and records actual kWh over days, capturing duty cycle and standby together. For anything you suspect is expensive, measuring beats every estimate including this one.