An elementary charge is the electrical charge carried by a single electron . This is equivalent, but opposite in polarity , to the electrical charge carried by a proton . By convention, electrons have negative (minus) charge, and protons have positive (plus) charge.
The unit of electrical charge quantity in the International System of Units is the coulomb . One coulomb (1 C) is equal to approximately 6.24 x 10 18 elementary charges. Thus, an elementary charge is approximately 1.60 x 10 -19 C.
Also see Table of Physical Units and Constants.