Watt (W)

Metric (SI)Current unit

The SI unit of power: one joule per second. A typical LED bulb uses 5–10 W and a laptop 30–60 W.

The watt is the reference unit for power on this site.

About the watt

Credit for the name goes to C. William Siemens, who proposed it in August 1882 in his presidential address to the British Association for the Advancement of Science. He chose it to honor James Watt, the Scottish inventor who in 1776 improved the Newcomen steam engine. An International Conference on Electric Units and Standards adopted Siemens' definition in London in October 1908 as the international watt. After the 1948 General Conference on Weights and Measures the unit was redefined in absolute terms, and in 1960 the 11th General Conference adopted it into the SI as the unit of power.

Today one watt is one joule per second, or equivalently one volt times one ampere. Orders-of-magnitude tables put an LED light bulb at about 7 W and an adult's basal metabolic rate at roughly 100 W. A 100 kg person climbing a 3 m ladder in 5 seconds works at about 600 W, while a laborer can sustain around 75 W over an eight-hour day. The watt measures a rate, so it says how fast energy is being used, not how much has been used in total.

Sources: Wikipedia: Watt; Wikipedia: Orders of magnitude (power)

Watt conversion chart

1 watt expressed in every other power unit:

More Metric (SI) units

• kilowatt (power)
• megawatt (power)
• gigawatt (power)
• milliwatt (power)
• metric horsepower (power)
• meter (length)
• kilometer (length)
• centimeter (length)
• millimeter (length)
• micrometer (length)
• nanometer (length)
• picometer (length)
• decimeter (length)
• hectometer (length)
• decameter (length)
• kilogram (weight & mass)

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