The ampere
SI Illustration Constants Colour A_e_delta nu BIPM

The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 x 10–19 when expressed in the unit C, which is equal to A s, where the second is defined in terms of ΔνCs.

Definition from the new SI.

Realization of the ampere in INRiM

The base unit ampere is realized indirectly, through the Ohm's law I=V/R, from the quantum realizations of the electrical units of voltage and resistance.


The other electrical units are traced to ohm and volt according to the following scheme.