WattWise

Estimate what your appliances really cost — kWh and money, per day, month and year.

The arithmetic is simple and the inputs are where people go wrong. Cost is power in kilowatts times hours of use times the tariff — but the plate rating on an appliance is its maximum draw, not its average, and anything thermostatic spends much of its time not drawing that at all.

Standby is the surprise. Devices that appear off can account for a noticeable share of a household bill, and the biggest consumers are usually the boring continuous ones — a fridge, a water heater — rather than the things that feel power-hungry because they are loud.