wattage

Wattage is the rate at which electrical energy is transferred, used, or produced by a device, expressed in watts (W). It is the SI unit of power, named after James Watt. In everyday use, wattage commonly signals how much energy a device consumes or how much power it can deliver. Light bulbs, heaters, motors, and electronic devices are typically labeled with a wattage rating to indicate their power requirements or capabilities.

Power calculations differ for direct current and alternating current. Real or active power, measured in watts, represents the portion of energy actually converted to useful work. In AC circuits with reactance, apparent power is given in volt-amperes (VA) and can exceed real power. The relationship is P = V × I × cos(phi) for AC, or P = V × I for DC, where phi is the phase angle between voltage and current; power factor describes efficiency of the circuit.

Energy use is the product of power and time. One kilowatt-hour is the energy consumed by a one-kilowatt device running for one hour. For example, a 60 W bulb used for 4 hours consumes 0.24 kWh. Wattage alone does not convey efficiency or brightness, which are better captured by lumen output and luminous efficacy.

Wattage is used at multiple scales, from watts (W) and kilowatts (kW) for household devices to megawatts (MW) for power plants and grids. Solar panels are rated by wattage under standard test conditions. Understanding wattage helps evaluate energy costs, electrical demand, and the design of circuits and lighting systems, alongside other electrical ratings.