Ampere (A)
A is the ampere, or amp, the SI unit of electric current. One ampere is one coulomb of charge flowing past a point each second.
Easily confused with
How to read it
OpenStax’s University Physics defines the ampere as one coulomb of charge passing through a given area per second, and names it after the French physicist André-Marie Ampère (1775–1836). It notes that circuit breakers at home and fuses in a car are rated in amps. Since 2019 the BIPM’s SI Brochure has defined the ampere from the elementary charge, fixed at exactly 1.602 176 634 × 10⁻¹⁹ coulombs, where a coulomb is an ampere second. On a meter the same A marks the current settings and jacks (A, mA and µA).
Also searched as: A, A in physics, ampere symbol, amps, amp symbol, unit of electric current.
One letter, three meanings
NIST’s Guide for the Use of the SI uses the letter A to show why type matters: an italic A is the quantity area, an upright A is the unit ampere, and a bold italic A is the vector potential. With a ring on top, Å is the ångström, a unit of length.
Read next
- Next in Physics and chemistry symbolsÅngström (Å)Å is the ångström, a unit of length: 0.1 nanometre, or 10⁻¹⁰ metre. It is used for the distances between atoms and for wavelengths of light. It is not an SI unit.
- The A on a multimeter’s dial is the ampere.Amps symbol (A, mA and µA)The current settings. A is amps, mA milliamps (thousandths of an amp) and µA microamps (millionths). A wave beside the letter means AC current, and a solid line over dashes means DC current.
More physics and chemistry symbols
The same shape elsewhere
Browse symbols drawn with letters and numbers.
Sources
- University Physics Volume 2, 9.1 Electrical Current, OpenStax (Rice University), Defining Current and the Ampere
- The International System of Units (SI), 9th edition, SI Brochure, 9th edition (2019), updated 2024, Bureau International des Poids et Mesures (BIPM), Sec. 2.3.1 The ampere; Appendix 1
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811 (2008), National Institute of Standards and Technology, Sec. 10.2
- Chemistry 2e, 1.4 Measurements, OpenStax (Rice University), Table 1.2
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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