How Much Does It Cost to Run an Appliance? Watts to Pounds

Watts Tell You Nothing About Cost

The number on an appliance label is power — the rate it draws electricity. What you pay for is energy: power multiplied by time. The two get confused constantly, and the confusion leads people to worry about the wrong things.

A 3 kW kettle sounds alarming and costs about 6p a boil, because it runs for five minutes. A 5 W streaming box sounds trivial and costs about £11 a year, because it never switches off. Power is only half the story; duration is the other half.

The Two-Step Calculation

Everything follows from one conversion and one multiplication:

1. Energy used: kWh = (Watts × Hours) ÷ 1,000
2. Cost: kWh × your unit rate

The division by 1,000 turns watts into kilowatts, which is the unit your bill is priced in.

A 2,000 W heater running 5 hours uses (2,000 × 5) ÷ 1,000 = 10 kWh. At roughly 25p per kWh that is £2.50 a day, or about £75 over a month.

What Everyday Things Actually Cost

Worked at about 25p per kWh:

Kettle (3 kW, 5 minutes): 6p a boil
LED bulb (9 W, 5 hours): 1.1p a day
Old incandescent bulb (60 W, 5 hours): 7.5p a day — roughly seven times more
Tumble dryer (2.5 kW, 2 hours): £1.25 a cycle
Fridge-freezer (around 200 kWh a year): about £50 a year
Electric heater (2 kW, 5 hours a day): about £75 a month

The pattern is clear: anything that produces heat dominates. Kettles, dryers, ovens, immersion heaters and electric heating are where the money goes, because turning electricity into heat takes a great deal of energy.

The Standing Charge You Pay Regardless

Unit rate is only part of the bill. A standing charge is levied every day whether you use any electricity or not, covering network maintenance and metering.

At around 60p a day that is roughly £219 a year before you switch anything on — and gas carries its own standing charge on top.

This is why a nearly empty flat still receives a bill, and why comparing tariffs on unit rate alone can mislead: a low unit rate paired with a high standing charge can cost a light user more overall.

Every Electric Heater Is 100% Efficient

This is the most useful thing on the page, and it saves people real money.

A £30 fan heater, a £100 convector and a £300 oil-filled radiator, all rated at 2 kW, cost exactly the same to run. Every one converts essentially 100% of the electricity into heat, because heat is what electrical resistance produces. There is nowhere else for the energy to go.

Marketing claims that one electric heater is cheaper to run than another at the same wattage are, physically, not possible. What genuinely differs is how the heat is delivered: a fan heater warms a room quickly and noisily, an oil-filled radiator warms it slowly and keeps radiating after switch-off, and thermostats and timers reduce cost by cutting running time rather than by being more efficient.

The One Real Exception

Heat pumps break this rule, because they move existing heat rather than creating it. With a coefficient of performance around 3 to 4, they deliver three to four units of heat per unit of electricity. That is not a violation of physics; it is the difference between generating heat and relocating it.

It is also why gas heating is usually cheaper to run than electric resistance heating: gas typically costs around a quarter of the price of electricity per kWh.

Standby Is Small but Free to Fix

A device drawing 5 W continuously uses about 43.8 kWh a year, roughly £11. One device is negligible; a household of a dozen televisions, consoles, chargers, printers and set-top boxes turns it into real money for no benefit at all.

It rarely justifies unplugging your fridge, but a switched extension lead for the television corner costs nothing to use and pays for itself.

Finding Your Own Numbers

The 25p per kWh used above is illustrative. Your actual rate is printed on your bill, and in Great Britain the Ofgem price cap is reviewed quarterly, so any figure quoted in an article dates quickly. Use your own.

Two further wrinkles are worth knowing. On Economy 7 and similar tariffs you pay a low night rate and a higher day rate, so when you run the dryer changes the cost. And appliance labels show maximum draw: a washing machine rated 2 kW only pulls that while heating water, so the average over a cycle is far lower. A plug-in energy monitor measures what a device actually uses rather than what its label claims.

Conclusion

Multiply watts by hours, divide by a thousand, multiply by your unit rate. That single chain answers every version of the question, and it consistently shows that heat is expensive and standby is quietly persistent. Put your own wattage, hours and tariff into an Electrical Power Calculator to price anything in your house — and remember that no 2 kW heater is cheaper to run than another 2 kW heater, whatever the box says.

Try our Electrical Power Calculator

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