What Is the Difference Between kW and kWh?
Last reviewed: 2026-06-14
Quick answer
kW measures power, or how fast energy moves. kWh measures energy, or how much energy is stored or used. EV charging estimates need both: charger kW tells you speed, and battery kWh tells you how much energy must be added.
kW is charging speed
A charger rated at 11 kW can move energy much faster than a 2.4 kW outlet, but the vehicle must be able to accept that power. On AC charging, the onboard charger limit may be lower than the wall unit, so the lower limit controls the estimate.
kWh is battery energy
A 75 kWh battery can store much more energy than a 40 kWh battery, so the same percentage change can mean different amounts of energy. Charging 50% of a 75 kWh pack adds about 37.5 kWh before efficiency losses.
How they work together
Charging time is roughly kWh needed divided by kW available, adjusted for efficiency and real-world limits. If you need 45 kWh and can average 9.9 kW into the battery, the session is about 4.5 hours before any extra buffer.
FAQ
Is kWh the same as kW per hour?
No. kWh is a unit of energy, not a rate of change. A 10 kW charger running for 2 hours can deliver about 20 kWh before losses, which is why both units appear together in charging estimates.