How do you convert watts to kWh?
Watts measure power, while kWh measure energy over time. Multiply watts by hours, divide by 1,000, then multiply by days and quantity. If you also want a dollar estimate, use the Electricity Cost Calculator.
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What operating time should you use?
Use the average hours each device runs per day and the number of days in the period. For cycling appliances where full rated power is not continuous, the Appliance Energy Cost Calculator adds a duty-cycle adjustment.
What does the kWh result represent?
The result is the modeled electrical energy used by all entered devices across the full period. You can price that energy with the kWh Cost Calculator or compare it with the kWh on a utility bill.
Where is watt-to-kWh conversion useful?
It is useful for estimating lighting, electronics, heaters and other loads when you know wattage and run time. For lighting replacement decisions, use the LED Lighting Savings Calculator; for total household energy planning, use the Home Energy Cost Calculator.
Worked example: Watt to kWh
Enter the following values in the Watt to kWh Calculator and calculate to reproduce this result.
- Power per device: 1000
- Hours used per day: 4
- Number of days: 30
- Number of devices: 1
Example result: 120 kWh. 1,000 watts × 4 hours/day × 30 days × 1 device equals 120 kWh.
Calculation used: kWh = watts × hours/day × days × quantity ÷ 1,000
How to interpret this example
Power must be multiplied by operating time to obtain energy. Here 1,000 × 4 × 30 ÷ 1,000 = 120 kWh for one device. It does not include a price until an electricity rate is applied separately.
Frequently asked questions about Watt to kWh
kWh = watts × hours × days × quantity ÷ 1,000.
One kilowatt equals 1,000 watts, so dividing watt-hours by 1,000 converts them to kilowatthours.
Yes. For example, 30 minutes can be entered as 0.5 hours.
Yes. Use the quantity field when the devices have the same wattage and operating schedule.
No. Many devices vary their power draw, so rated wattage and average real-world power can differ.
No. This tool converts power and time to energy. Use the kWh Cost Calculator to price the result.
For solar sizing, use the Solar Panel Calculator because solar output depends on peak sun hours and system efficiency.
No. kWh is a unit of energy; watts and kilowatts are units of power.
Sources and methodology
The calculator uses the transparent formula described on this page and the values you enter. These authoritative U.S. resources provide context for electricity, home energy, solar, efficiency or safety topics related to this tool.