kilowatthours

Kilowatt-hours (symbol kWh) are a unit of energy commonly used to quantify electrical energy. A kilowatt-hour represents the amount of energy produced or consumed when a device with a power of one kilowatt operates for one hour. It is equal to 1000 watt-hours, or 3.6 million joules (3.6 MJ); since 1 watt-hour equals 3600 joules, 1 kWh = 1000 × 3600 J.

Kilowatt-hours are distinct from kilowatts (kW), which measure rate of energy transfer or power, not total energy. In practical terms, the kWh is the unit utilities use to bill electricity consumption, and meters record usage in kWh. It is convenient for expressing how much energy a device uses over time.

Examples illustrate the concept: a 100 W light bulb running for 10 hours consumes 1 kWh (0.1 kW × 10 h = 1 kWh). A 2 kW kettle used for 0.5 hours also uses 1 kWh (2 kW × 0.5 h = 1 kWh).

Common multiples include 1 MWh = 1000 kWh and 1 GWh = 1,000,000 kWh. The kilowatt-hour is not an SI base unit; the SI unit of energy is the joule, but the kWh is widely used and accepted for use with the SI, especially in electricity energy contexts.