Electricity Cost Calculator

The arithmetic, once

A watt is a rate, and a kilowatt-hour is a quantity: one thousand watts drawn for one hour. So a 1,500 W heater run for three hours uses 4.5 kWh, and at 17 cents that is 76 cents. Everything else on this page is that same calculation extended over days and years.

The useful consequence is that cost is driven by the product of power and time, and people consistently misjudge which of the two dominates. A 2,000 W kettle sounds alarming and runs for three minutes. A 40 W aquarium pump sounds trivial and runs for 8,760 hours a year, using nearly twice as much electricity.

Where household electricity actually goes

In most homes, heating and cooling dominate, followed by water heating, then the refrigerator, then everything else together. Electric resistance heating is in a category of its own: a single 1,500 W space heater run through a winter can add more to a bill than every consumer electronic device in the house combined. If a bill has jumped, look first at anything that makes heat — heaters, dryers, kettles, ovens, hot water — because heat is where the kilowatts are.

Standby is real but small

Devices left plugged in draw something continuously, and because it runs all year it is not nothing: a household typically loses one to five percent of its bill this way. But the effort-to-saving ratio is poor compared with the heating items above, and unplugging a phone charger achieves almost literally nothing. The exceptions worth attention are set-top boxes, older games consoles and anything with a permanently warm power brick.

Your rate is probably not one number

Many tariffs charge different rates at different times of day, and some add a tiered rate that rises once you pass a monthly threshold. If you are on a time-of-use tariff, the number that matters for a dishwasher or a dryer is the off-peak rate, and shifting those loads is often worth more than reducing them. Take the figure from a bill rather than from memory: divide the total by the kilowatt-hours used, which also captures standing charges and gives you what electricity genuinely costs you.

Watts on the label are a maximum, not an average

A rating plate shows peak draw. A fridge rated at 150 W does not use 150 W continuously — its compressor cycles, and the real average might be a third of that. Thermostatically controlled devices, including heaters and air conditioners, all behave this way. For anything that cycles, the figure here is an upper bound, and a plug-in energy monitor is the only way to get the true number.