How do I work out what an appliance costs to run?
One piece of arithmetic that turns speculation about which appliance is expensive into a number.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 2 min
Short answer
Watts divided by 1,000, times hours used, times your unit rate. A 2,000W heater for three hours at 25p per kilowatt hour costs £1.50. Everything else is refinement.
Most household discussion of energy is guesswork, and the calculation is genuinely simple. Doing it once for the three or four things you were unsure about usually reorders people's assumptions completely.
Step by step
- Find the appliance's power rating.In watts, on a label on the back or underneath, or in the manual. Some list amps instead — multiply amps by 230 for an approximate wattage.
- Find your unit rate.Pence per kilowatt hour, on your bill. Electricity and gas are charged at different rates, so use the right one.
- Do the calculation.(Watts ÷ 1000) × hours × unit rate. So 2,000W for 3 hours at 25p = 2 × 3 × 25 = 150p, or £1.50.
- Adjust for things that cycle.Fridges, freezers, kettles and heating do not run constantly at full power. A fridge rated 100W might average a fraction of that. Use the annual kWh figure on the energy label for these instead.
- Use the energy label for large appliances.Washing machines, dishwashers, fridges and ovens carry an annual or per-cycle kWh figure. Multiply by your unit rate — far more accurate than the wattage for anything with a cycle.
- Measure it if you want certainty.A plug-in energy monitor costs very little and shows actual consumption over time. It settles arguments and frequently produces surprises.
- Focus on heat, then on time.Anything that heats — kettle, oven, tumble dryer, electric heater, shower — uses far more than anything electronic. And a low-power device left on all year can still add up.
- Check standby honestly.Modern standby is usually small, but a handful of older devices are not. A monitor tells you which, rather than turning everything off on principle.
Tips
- Gas is typically much cheaper per kilowatt hour than electricity, which is why heating and cooking costs differ so much between fuels.
- The three big domestic electricity users are almost always heating, hot water and the tumble dryer. Start there.
- A plug-in monitor borrowed or bought once tells you more than a year of speculation. Some libraries lend them.
Questions people ask
How do I calculate what an appliance costs to run?
Watts divided by 1,000, multiplied by hours used, multiplied by your unit rate in pence. For anything that cycles, use the annual kWh figure on the energy label instead.
What uses the most electricity in a house?
Almost always things that generate heat — electric heating, hot water, the tumble dryer, the oven and the kettle. Electronics are usually a small fraction.