 In the 2019 redefinition of SI base units, 4 ×  is the value for based upon more accurate measurements of the fine structure constant.In electrostatic cgs units, the unit of electric charge, the statcoulomb, is defined so that the Coulomb constant, , or the permittivity factor, , is 1 and dimensionless.Then the expression of the fine-structure constant, as commonly found in older physics literature, becomes

In natural units, commonly used in high energy physics, where , the value of the fine-structure constant is
As such, the fine-structure constant is just another, albeit dimensionless, quantity determining (or determined by) the elementary charge