The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Ohm. Various empirically derived standard units for electrical resistance were developed in connection with early telegraphy practice, and the British Association for the Advancement of Science proposed a unit derived from existing units of mass, length and time, and of a convenient scale for practical work as early as 1861. As of 2020, the definition of the ohm is expressed in terms of the quantum Hall effect.

A laboratory one-ohm standard resistor, circa 1917.
General information
Unit systemSI derived unit
Unit ofElectrical resistance
Named afterGeorg Ohm
DerivationΩ = V/A
1 Ω in ...... is equal to ...
   SI base units   kgm2s−3A−2