Watt-Hour (Wh)
Unit of energy equal to one watt of power sustained for one hour, or 3,600 joules. Watt-hours and their multiple the kilowatt-hour are the standard units for metering electricity, and have become the conventional way to report the energy intensity of digital services such as LLM queries and web searches.
A watt-hour (Wh) is a unit of energy equal to one watt of power sustained for one hour, or 3,600 joules. It is the standard unit used by utilities and consumers to measure electricity consumption, most commonly in its larger multiple, the kilowatt-hour (kWh, 1,000 Wh). To build intuition: a typical incandescent lightbulb of 60 W draws 60 Wh over one hour; a modern LED lamp draws roughly 10 Wh. A smartphone battery holds about 10-20 Wh, a laptop battery 40-100 Wh, and an average single-family home in industrialised countries consumes on the order of 20-30 kWh per day. Electric vehicle batteries are commonly sized in the 40-100 kWh range. The watt-hour has become the conventional unit for discussing the energy intensity of digital services: web searches, video streams, cryptocurrency transactions, and large language model queries are typically reported in Wh per request. Because the underlying physical quantity is energy rather than power, watt-hours can be added across devices and time periods, which makes them convenient for life-cycle analyses and carbon footprint accounting when combined with the local grid emissions factor.