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.
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.