The elementary charge, \(e\), is one of seven fixed constants defining the International System of Units, the SI, with \(e = 1.602\ 176\ 634\ \times 10^{-19}\ \text{C}\). The elementary charge \(e\) corresponds to a coupling strength of the electromagnetic force via the fine-structure constant and is considered as a fundamental constant of nature.
BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 127ff [Terms] [Book]
Newell et al., Metrologia 55, L13-L16 (2018) [Terms] [Source]