| ohm | |
|---|---|
 A laboratory one-ohm standard resistor, c. 1917 | |
| General information | |
| Unit system | SI |
| Unit of | electrical resistance |
| Symbol | Ω |
| Named after | Georg Ohm |
| Conversions | |
| 1 Ω in ... | ... is equal to ... |
| SI base units | kg⋅m2⋅s−3⋅A−2 |
The ohm (symbol: Ω, the uppercase Greek letter omega) is the unit of electrical resistance in the International System of Units (SI). It is 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.
Following the 2019 revision of the SI, in which the ampere and the kilogram were redefined in terms of fundamental constants, the ohm is now also defined as an exact value in terms of these constants.