SI coherent derived unit with special name and symbol
Name Symbol Derived quantity Expressed in terms of SI base units
coulomb C electric charge s A


The coulomb, symbol C, is the SI coherent derived unit of electric charge.

One coulomb is the charge transported by a constant current of one ampere in one second.

The coulomb is named after the French physicist, Charles-Augustin de Coulomb (1736 – 1806).

The fixed numerical value of the elementary charge, e, is defined as 1.602 176 634 × 10−19 C. This definition implies the exact relation e = 1.602 176 634 × 10−19 C. Inverting this relation gives an exact expression for the coulomb in terms of the defining constant e:

e \mspace{19mu} = 1.602\ 176\ 634 \times 10^{-19} \ \text{C}\\ \\ \\ 1 \ \text{C} = \dfrac{e}{1.602\ 176\ 634 \times 10^{-19}}

The effect of this definition is that one coulomb is exactly 1/(1.602 176 634 × 10−19) of the value of the elementary charge, e.


One coulomb is the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt.