SI REFERENCE POINT
Version: 1.0 Beta , last update: 2025-01-31

ampere

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to ${2 \times 10^{-7}}$ newton per metre of length.

This definition is valid from 1948-01-01 to 2019-05-19
Unit ampere
Symbol A
Quantity electric current
Defining Resolution
CGPM Resolution 2 (1948)
Unit Type SI base unit
Notes:
  1. The expression « MKS unit of force » which occurs in the original text has been replaced here by «newton», a name adopted for this unit by the 9th CGPM (1948, Resolution 7).