Plain-English glossary
Energy Cost Glossary
Use this glossary when an energy bill, appliance label or calculator asks for watts, hours, kWh or price per kWh. The terms explain what each input means before you estimate running cost.
What this glossary is for
Energy cost estimates are easy to misread because power and energy are related but not the same. Watts describe how fast a device uses electricity. Kilowatt-hours describe the amount used over time. Cost appears only after the kWh amount is multiplied by your electricity price.
Key terms
Watt (W)
A watt is a measure of power. It tells you how quickly a device uses electricity at a moment in time. A 1000 W heater uses electricity much faster than a 10 W lamp.
Kilowatt (kW)
A kilowatt is 1000 watts. Converting watts to kilowatts is useful because electricity billing usually uses kilowatt-hours.
Kilowatt-hour (kWh)
A kWh is energy used over time. A 1 kW device running for 1 hour uses 1 kWh. A 0.5 kW device running for 2 hours also uses 1 kWh.
Electricity rate
The price you pay for each kWh. The calculator needs this rate to turn energy use into estimated cost.
Running cost
The estimated cost of using a device for a chosen number of hours and days.
Standby power
Electricity used while a device is not actively being used but remains plugged in or ready.
Duty cycle
How often a device is actively drawing power. Fridges and freezers cycle on and off, so their label wattage may not mean they use that power every minute.
How to use the terms
Read the definition first, then open the calculator that uses the same term. Change one input at a time so you can see which number drives the result.
Main related calculator
The first tool below is the most directly related calculator for this glossary. The remaining links stay within the same topic so the page does not send visitors into unrelated tools.