Energy Cost Calculator
Work out what an appliance costs to run from its wattage, how long you use it, and your electricity unit price.
watts (W)
pence per kWh
Cost to run
£1.50/day
6.00 kWh per day
- Weekly cost
- £10.50
- Monthly cost
- £45.50
- Annual cost
- £546.00
How is the cost of electricity calculated?
Electricity is billed per kilowatt-hour (kWh), also called a "unit". A kWh is the energy used by a 1,000-watt (1 kW) appliance running for one hour. To find a cost, multiply the appliance's power in kilowatts by the hours it runs and by your unit price.
Enter the wattage (shown on the appliance or its label), how many hours a day you use it and your electricity price in pence per kWh. The calculator converts watts to kilowatts for you and shows the daily, weekly, monthly and annual cost.
Finding your unit price
Your electricity unit price is on your bill or in your online account, quoted in pence per kWh. Under the price cap it has typically been in the region of 25 to 30p per kWh, but it varies by tariff, region and over time, so use your own figure for accuracy.
High-wattage appliances used for long periods (heaters, tumble dryers, ovens) dominate energy bills, so they are the best place to look for savings.
Worked example
A 2,000-watt (2 kW) electric heater used for 3 hours a day at 25p per kWh uses 6 kWh a day, costing £1.50 a day.
Over a month that is about £45, and used every day for a year it would cost roughly £547.
Frequently asked questions
Where do I find an appliance's wattage?
It is usually printed on a label on the appliance or in its manual, shown in watts (W) or kilowatts (kW). 1 kW equals 1,000 W.
What unit price should I use?
Use the pence-per-kWh figure from your electricity bill or online account for your tariff, as prices vary by supplier and region.
Does this work for gas?
This calculator is for electricity. Gas is also billed per kWh but appliances are rated differently, so the wattage method does not apply directly.
Why is my real bill higher?
Your bill also includes a daily standing charge and every appliance in your home, not just the one you calculated here.
How can I cut the cost?
Focus on high-wattage items used for long periods, reduce runtime, and compare tariffs. Small, quick-use appliances usually cost very little.
Figures last reviewed on 13 August 2025.
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