K_J = 2e/h (where e is the elementary charge and h is the Planck constant), a "conventional" value K_J-90 = was used for the purpose of defining the volt. As a consequence of the 2019 revision of the SI, as of 2019 the Josephson constant has an exact value of = , which replaced the conventional value K_J-90.

This standard is typically realized using a series-connected array