Kilowatts times hours times your unit rate. Divide the watts on the rating plate by 1,000, multiply by hours used, multiply by pence per kWh.
- Find the watts. It is on the rating plate, usually on the back, the base or inside the door.
- Divide by 1,000 to get kilowatts. A 2,500W tumble dryer is 2.5kW.
- Multiply by the hours it runs. A 90 minute cycle is 1.5 hours, so 3.75 kWh.
- Multiply by your unit rate in pence. At 26.11p that is 97.9p per cycle.
- Multiply by how often you use it for a weekly or annual figure.
Appliances that cycle on and off, such as fridges, freezers, ovens and dishwashers, do not draw their plate rating continuously. Multiplying a 200W fridge by 24 hours overstates its cost by roughly threefold, and it is the commonest error in published running-cost figures.
This one sum is the whole of domestic energy arithmetic. Everything on a running-cost page is this calculation with the assumptions stated, which is why every page here shows its working instead of asserting a number.
Energy figures are worked from the Ofgem price cap on the date shown and from typical power for the appliance class, not from a named model. Your own rate and your own rating plate are the ones that count. Full disclaimer.