Leeds and Northrup one ohm standard resistance.jpg
A laboratory one-ohm standard resistor, circa 1917.
General information
Unit systemSI derived unit
Unit ofElectrical resistance
Named afterGeorg Ohm
In SI base units:kgm2s−3A−2

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


A multimeter can be used to measure resistance in ohms, among other things.

The ohm is defined as an electrical resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force.[1]

in which the following units appear: volt (V), ampere (A), siemens (S), watt (W), second (s), farad (F), henry (H), joule (J), kilogram (kg), metre (m), and coulomb (C).

In many cases the resistance of a conductor in ohms is approximately constant within a certain range of voltages, temperatures, and other parameters. These are called linear resistors. In other cases resistance varies (e.g., thermistors).

A vowel of the prefixed units kiloohm and megaohm is commonly omitted, producing kilohm and megohm.[2]

In alternating current circuits, electrical impedance is also measured in ohms.

Other Languages
Afrikaans: Ohm
العربية: أوم
অসমীয়া: ওম
asturianu: Ohmiu
azərbaycanca: Om (ölçü vahidi)
বাংলা: ওহম
беларуская (тарашкевіца)‎: Ом
български: Ом (физика)
བོད་ཡིག: ཨོ་མུ།
bosanski: Om
brezhoneg: Ohm
català: Ohm
čeština: Ohm
Cymraeg: Ohm
dansk: Ohm
Deutsch: Ohm
eesti: Oom
español: Ohmio
Esperanto: Omo
euskara: Ohm
فارسی: اهم
français: Ohm (unité)
Gaeilge: Óm
Gaelg: Ohm
galego: Ohm
한국어: 옴 (단위)
hrvatski: Om
Bahasa Indonesia: Ohm
íslenska: Ohm
italiano: Ohm
עברית: אוהם
ქართული: ომი (ფიზიკა)
қазақша: Ом
Кыргызча: Ом
latviešu: Oms
lietuvių: Omas
Limburgs: Ohm (einheid)
македонски: Ом
मराठी: ओह्म
Bahasa Melayu: Ohm
монгол: Ом
မြန်မာဘာသာ: အုမ်း
Nederlands: Ohm (eenheid)
日本語: オーム
Nordfriisk: Ohm (ianhaid)
norsk: Ohm
norsk nynorsk: Ohm
occitan: Ohm
oʻzbekcha/ўзбекча: Om
ਪੰਜਾਬੀ: ਓਹਮ
پنجابی: اوہم
Patois: Uom
Piemontèis: Ohm
Plattdüütsch: Ohm (Eenheit)
português: Ohm
română: Ohm
русский: Ом
Scots: Ohm
sicilianu: Ohm
සිංහල: ඕම්
Simple English: Ohm
slovenčina: Ohm (jednotka)
slovenščina: Om
српски / srpski: Ом (јединица)
srpskohrvatski / српскохрватски: Om (jedinica)
suomi: Ohmi
svenska: Ohm
ไทย: โอห์ม
Türkçe: Ohm
українська: Ом
اردو: اوھم
Tiếng Việt: Ohm
Winaray: Ohm
粵語: 歐姆
中文: 歐姆