kW to kWh Calculator (and kWh to kW)
Kilowatts (kW) measure power, the rate at which energy is used. Kilowatt-hours (kWh) measure energy used over time. To convert between them you need the time involved.
How it works
Energy (kWh) = power (kW) × time (hours). Power (kW) = energy (kWh) ÷ time (hours). Time (hours) = energy (kWh) ÷ power (kW). 1 kW = 1,000 W, and 1 kWh = 3.6 megajoules exactly (NIST).
Worked example: EIA's example: a 40 W (0.04 kW) light bulb used for 5 hours uses 0.04 × 5 = 0.2 kWh (200 Wh). A charger delivering 7.2 kW for 8 hours supplies 7.2 × 8 = 57.6 kWh.
Assumptions
- Power is constant over the period. If power varies (for example an EV charging session that tapers), enter the average power.
- kW cannot be converted to kWh on its own: the answer always depends on how long the power is used.
- For EV charging, energy drawn from the charger is a little more than the energy stored in the battery because of charging losses; see the charging time calculator.
Frequently asked questions
What is the difference between kW and kWh?
The U.S. Energy Information Administration explains that watts measure power at a specific moment, while watthours measure how much electricity is used over a period of time. One kWh is one kilowatt for one hour.
How many kWh is 1 kW?
1 kW used for 1 hour is 1 kWh; for 10 hours it is 10 kWh. Without a time period there is no single conversion.
How much energy does a 7.2 kW charger deliver in one hour?
7.2 kWh per hour at full output. The U.S. DOE Alternative Fuels Data Center says most residential Level 2 chargers operate at up to 30 amps, delivering 7.2 kW. Energy stored in the battery is slightly less because of charging losses.
Related calculators
- Watts, volts and amps calculator
- EV charging time calculator
- EV charger amps to kW chart
- kWh to BTU, joules and therms converter
- EV charging cost calculator
Sources
Formulas and reference values are from these sources. Page last reviewed 2026-10-19.