In physics, the weber (symbol: Wb;  /ˈveɪbər/, /ˈwɛbər/, or /ˈwiːbər/) is the SI unit of magnetic flux. A flux density of one Wb/m² (one weber per square meter) is one tesla.

The weber is named for the German physicist Wilhelm Eduard Weber (1804–1891).

The weber may be defined in terms of Faraday's law, which relates a changing magnetic flux through a loop to the electric field around the loop. A change in flux of one weber per second will induce an electromotive force of one volt (produce an electric potential difference of one volt across two open-circuited terminals).

Officially,

Weber (unit of magnetic flux) — The weber is the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.

In SI base units, the dimensions of the weber are (kg·m²)/(s²·A). The weber is commonly expressed in terms of other derived units as the Tesla-square meter (T·m²), volt-seconds (V·s), or joules per ampere (J/A).

Unit may refer to: