Kilowattimmar

Kilowattimmar (kWh) is a unit of energy most commonly used to quantify electrical energy in households and industry. It expresses how much energy is transferred or consumed when a load with a power of one kilowatt operates for one hour.

The energy E in kilowatt-hours relates to power P and time t by E = P × t, with P in kilowatts and t in hours. Since 1 kilowatt equals 1000 watts and 1 hour equals 3600 seconds, 1 kWh equals 3,600,000 joules (3.6 MJ). The kilowatt-hour is not an SI unit, but it is a widely used practical unit for billing and energy planning. About 1 kWh is roughly the energy content of 860 kilocalories.

In everyday use, electricity suppliers bill customers for the number of kilowatt-hours consumed. Electric meters, including smart meters, typically record energy in kWh. Appliance energy labels and annual consumption estimates are expressed in kWh. Battery capacities are often stated in kilowatt-hours, indicating how much energy a battery can store.

Examples help illustrate the concept: a 100-watt bulb left on for 10 hours consumes about 1 kWh (0.1 kW × 10 h). A 2-kW space heater running for 3 hours uses about 6 kWh. A typical household might use hundreds to several thousand kWh per month, depending on climate and usage.

Kilowatt-hours are standard in many countries, including most of Europe; they provide a convenient measure for comparing efficiency and cost of electrical devices and energy services.