What Your Appliances Actually Cost to Run

An electricity bill arrives as one number, which is why nobody knows which appliance caused it. The arithmetic that breaks it apart is short, and once you have done it twice you can do the rest in your head.

The only formula you need

Watts times hours, divided by 1,000, gives kilowatt-hours. That is the unit your supplier charges for. A 60 W lamp left on for 10 hours uses 600 watt-hours, or 0.6 kWh. At 17 cents a unit that is about 10 cents. Leave it on every evening for a year and it comes to around $37.

The division by 1,000 is where people slip. Appliances are labelled in watts, bills are priced in kilowatt-hours, and forgetting the conversion makes everything look a thousand times worse than it is.

Where to find the wattage

Look at the rating plate: back of a fridge, underside of a kettle, on the power brick of anything with an external supply. It will say something like 1200W, or give volts and amps instead. If you see 230V and 8A, multiply them for 1,840 W. American plates often read 120V and 12.5A, which is 1,500 W.

Heating elements draw their full rating the whole time they are on. Motors and compressors cycle, so a fridge plated at 150 W might average 40 W across a day. For those, a plug-in energy monitor beats the label.

Two worked examples

A US space heater, 1,500 W, on 6 hours a day through a cold month: 1,500 x 6 divided by 1,000 is 9 kWh a day. At 17 cents that is $1.53 a day and $45.90 over 30 days. One appliance, and it is visible on the bill.

A UK tumble dryer using about 2.5 kWh a cycle, run four times a week, is 10 kWh a week. At 25p a unit that is £2.50 a week and £130 a year. Drying two of those loads on a rack instead saves roughly £65.

Compare either with a phone charger at 5 W. Three hours a night is 0.015 kWh, so about 5.5 kWh across a year, which is 93 cents at the same 17 cent rate. Worth knowing before you go round unplugging chargers while the dryer runs.

How to use the electricity calculator

Enter the wattage from the rating plate, the hours per day you actually use the thing, and your unit rate. The rate is on your bill, usually shown as a price per kWh. In the US, dividing the total charge by the kWh used gives a truer figure than the supply rate alone, because delivery charges are real money. In the UK it is the p/kWh line, kept separate from the daily standing charge.

Set the period to 30 days for a monthly figure or 365 for an annual one. Run the same appliance twice with different hours to see what cutting back is worth. If you are sizing heating or cooling rather than costing it, the air conditioner sizing guide starts in BTUs and converts to watts afterwards.

Common questions

Does leaving things on standby really cost anything? A little. A TV drawing 1 W draws it for all 8,760 hours of the year, which is 8.76 kWh, or $1.49 at 17 cents. Fifteen such devices come to roughly $22 a year: real money, but never the reason a bill doubled.

What uses the most electricity in a normal home? Anything that heats or cools. Electric heating, hot water, tumble dryers, ovens and air conditioning sit at the top. Lighting and electronics are usually a small slice, especially since LED bulbs took over.

Why is my bill higher than my calculation? Standing charges, taxes, and appliances you forgot. Add up your estimates and compare the total with the kWh figure on the bill. The gap tells you how much is running without you noticing.

How much does charging an electric car add? Enough to change the shape of your bill. A 60 kWh battery taken from 20% to 80% draws about 36 kWh, roughly $6 at 17 cents. The EV charging cost breakdown compares home rates with public chargers.