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Energy and power bills
Beginner
Kilowatt-hours measure household energy use.
1 kWh = 3.6 MJUtility companies charge for energy in kWh. Cost = power (kW) × time (h) × price.
A 1.5 kW heater for 4 h at 12 c/kWh: 6 kWh, 72 cents.
A kWh is not a unit of power.
In more detail
Electricity bills charge for energy in kilowatt hours. To estimate cost, multiply the power of an appliance in kilowatts by the hours it runs and by the price per unit.
Real-world uses
- Estimating the cost of running a 2 kW heater for 3 hours a day.
- Comparing the running costs of old and new appliances.
- Electricity bills charge for kilowatt-hours, so a 2 kW heater running for 3 hours uses 6 kWh of energy.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
How do I work out the cost of an appliance?
Power in kW times hours of use times the price per kWh.
Why do standby devices matter?
They draw small powers continuously, which adds up over a year.
How do I estimate the cost of using an appliance?
Multiply its power in kilowatts by hours of use, then by the price per kilowatt-hour.
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