Turn average power and operating time into energy. The same physical units work in the US, UK, India, Pakistan, Australia and Canada.
Quick answer
Energy in kWh equals power in kW multiplied by operating hours. A 150 W appliance running for 8 hours uses 1.2 kWh. One kWh is exactly 3.6 MJ. Power alone cannot be converted into energy without a duration.
Notes updated 2026-10-06
- Best for
- Checking appliance, charger or measured electricity use in any country.
- Inputs needed
- average power, power unit, operating hours
What is the difference between kW and kWh?
Kilowatts describe the rate of power use or generation. Kilowatt-hours describe energy accumulated over time. A battery stores kWh but has a separate kW output limit. A solar array has a kW rating; its daily kWh output depends on sunlight and losses.
Worked example: compare operating hours
| Average power | Duration | Energy |
|---|
| 15 W router | 24 hours | 0.36 kWh |
| 150 W appliance | 8 hours | 1.2 kWh |
| 7.2 kW charger | 4 hours | 28.8 kWh |
Using energy units with your electricity bill
The conversion is independent of country and currency. To estimate cost, multiply kWh by the applicable local price per kWh. Tier pricing, export credit, fixed charges and time-of-use windows require separate calculations.
Unit reference
The watt is a joule per second; the hour contains 3,600 seconds. See the BIPM SI Brochure for the physical units. Calculation content updated October 6, 2026.
Sources behind this estimate
Use the method references below to check the formula and its limitations. Input defaults and illustrative scenarios are not current tariffs, guaranteed output or live installer quotes.
Utility export rates, eligibility rules, and installer pricing can change. Confirm the applicable tariff, interconnection requirements, and tax treatment before making a purchase decision.
Frequently asked questions
How do I convert kW to kWh?+
Multiply average power in kW by operating hours. A 2 kW load running for 3 hours consumes 6 kWh.
How do I convert watts into kWh?+
Divide watts by 1,000, then multiply by hours. For example, 150 W for 8 hours is 1.2 kWh.
Does a 5 kW solar array produce 5 kWh every hour?+
Only when output averages 5 kW over that hour. Cloud, temperature, shade and inverter limits change output; panel rating alone cannot establish daily generation.
What is one unit of electricity on my bill?+
Where the bill defines a unit as a kilowatt-hour, one unit is 1 kWh. Check the meter and bill unit label; fixed charges, taxes and tier rates are separate from energy units.
How many megajoules are in one kWh?+
One kWh is exactly 3.6 megajoules: 1,000 joules per second multiplied by 3,600 seconds equals 3,600,000 joules.
Should I use an appliance nameplate or measured power?+
Measured average power gives a better energy estimate. Nameplate power can describe maximum draw; refrigerators and heat pumps cycle and rarely operate at that power continuously.