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Ampere - Wikipedia

Ampere

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The ampere (/ˈæmpɛər/AM-pair, US:/ˈæmpɪər/AM-peer;¹²³ symbol: A),⁴ often shortened to amp,⁵ is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 coulomb (C) moving past a point per second.⁶⁷⁸ It is named after French mathematician and physicist André-Marie Ampère (1775–1836), considered the father of electromagnetism along with Danish physicist Hans Christian Ørsted.

As of the 2019 revision of the SI, the ampere is defined by fixing the elementary charge e to be exactly 1.602 176 634 × 10${}^{-19}$ C,⁶⁹ which means an ampere is an electric current equivalent to 10${}^{19}$ elementary charges moving every 1.602 176 634 seconds, or approximately 6.241 509 074 × 10${}^{18}$ elementary charges moving in a second. Prior to the redefinition, the ampere was defined as the current passing through two parallel wires 1 metre apart that produces a magnetic force of 2 × 10${}^{-7}$ newtons per metre.

The earlier CGS system has two units of current, one structured similarly to the SI’s and the other using Coulomb’s law as a fundamental relationship, with the CGS unit of charge defined by measuring the force between two charged metal plates. The CGS unit of current is then defined as one unit of charge per second.¹⁰

Printed 2026-06-28.

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Footnotes

1. Jones, Daniel (2011), Roach, Peter; Setter, Jane; Esling, John (eds.), Cambridge English Pronouncing Dictionary (18th ed.), Cambridge University Press, ISBN 978-0-521-15255-6 ↩

2. Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Harlow: Pearson Education, ISBN 978-1-4058-8118-0 ↩

3. “ampere”, Merriam-Webster.com Dictionary, Merriam-Webster, OCLC 1032680871, retrieved 29 September 2020 ↩

4. “2. SI base units”, SI brochure (8th ed.), BIPM, archived from the original on 7 October 2014, retrieved 19 November 2011 ↩

5. SI supports only the use of symbols and deprecates the use of abbreviations for units. “Bureau International des Poids et Mesures” (PDF), 2006, p. 130, archived from the original (PDF) on 14 August 2017, retrieved 21 November 2011 ↩

6. BIPM (20 May 2019), “Mise en pratique for the definition of the ampere in the SI”, BIPM, retrieved 18 February 2022 ↩ ↩²

7. “2.1. Unit of electric current (ampere)”, SI brochure (8th ed.), BIPM, archived from the original on 3 February 2012, retrieved 19 November 2011 ↩

8. “Base unit definitions: Ampere”, Physics.nist.gov, archived from the original on 25 April 2017, retrieved 28 September 2010 ↩

9. Draft Resolution A “On the revision of the International System of units (SI)” to be submitted to the CGPM at its 26th meeting (2018) (PDF), archived from the original (PDF) on 29 April 2018, retrieved 28 October 2018 ↩

10. Bodanis, David (2005), Electric Universe, New York: Three Rivers Press, ISBN 978-0-307-33598-2 ↩

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