How much power an appliance draws and what it costs to run.
Divide the wattage by a thousand to get kilowatts, multiply by the hours it runs and by the price of a kilowatt-hour. A two-thousand-watt heater running five hours a day at 0.20 EUR costs two euro a day, or sixty a month.
A single device on standby draws 0.5–3 watts, or 4–26 kilowatt-hours a year. A household with a television, console, router, microwave and several chargers adds up to 50–100 kilowatt-hours a year — about twenty euro.
Anything that heats or cools: electric heating, the water heater, a tumble dryer, the hob, and the fridge, which draws little but never stops. Lighting and electronics are now a small share, since an LED bulb uses a tenth of an incandescent one.
No, because you pay for energy — power times time — not for power. A kettle twice as powerful boils water twice as fast and uses the same energy. A difference appears only when the more powerful device runs as long or longer than the weaker one.