How to compare appliance electricity costs
Use this guide to compare variable electricity costs for two devices or habits. Open the calculator.
Read the right number from your bill
Use your electricity unit rate per kWh, with tax included if that is how you want the estimate shown. Select pence for a price such as 25p/kWh, or pounds for £0.25/kWh. Both represent the same price. Do not enter a daily standing charge in the unit-rate field.
The formula
Energy in kWh = watts ÷1,000 × hours per day × days. Variable cost = kWh × price per kWh in pounds. The displayed difference is option A minus option B.
Worked examples
Illustrative prices only:1,000 W ×2 hours ×30 days =60 kWh. At 25p/kWh this is £15. A 600 W device at the same use and price consumes36 kWh and costs £9. The variable-cost difference is£6. This does not establish equal heat, brightness or comfort.
A 200 W desktop used 8 hours/day for 30 days consumes 48 kWh; at 30p/kWh it costs £14.40. A 50 W laptop under the same use consumes 12 kWh and costs £3.60. These invented example powers and prices are not measurements or current tariffs.
When the estimate is not enough
Rated power is not always average power. Thermostats, fridges, heat pumps and variable loads cycle on and off. Use measured average consumption where possible. This calculator does not compare device efficiency, purchase costs, standing charges, tiered tariffs or charging losses. For a multi-rate tariff, calculate each usage period separately; it does not automatically blend rates. A lower entered wattage need not do the same job.
Sources and review
Method reviewed 12 October 2026. Ofgem explains the difference between unit rates and standing charges. Citizens Advice also offers an appliance comparison tool. These links are reference sources, not endorsements or partnerships. We provide no current tariff database.