Kilowatt-Hour

Definition

The unit on your electricity bill — the energy used by running a 1000-watt appliance for one hour.

$1\ \text{kWh} = 3.6 \times 10^6\ \text{J}$

Symbol: $kWh$ · Unit: kilowatt-hour (kWh) — a unit of energy

Technical definition

A unit of energy equal to 3.6 megajoules: 1 kWh = 1000 W × 3600 s. Despite the name, it measures energy (like joules), not power — it is power multiplied by time.

Example

A 100 W bulb burning for 10 hours uses 1 kWh — roughly 15 cents of electricity in much of the US. An electric car battery holding 60 kWh stores the same energy as running that bulb for 600 hours.

Common confusion

A kilowatt-hour is not kilowatts per hour. The kilowatt (kW) is power — the rate; the kilowatt-hour (kWh) is energy — the total. A 2 kW heater running for 30 minutes uses 1 kWh, exactly the same as a 1 kW heater running for a full hour. Mixing them up makes electricity bills unreadable.