Are physical constants, such as the elementary charge or the gravitational constant, subject to Heisenberg uncertainty principle, theoretically and empirically? Theoretically in the sense that infinite precision of these constants will directly violate HUP. Empirically in the sense that, for instance, the mass of an object cannot be determined to infinite precision so the gravitational constant, which is calculated from masses, cannot too. Some constants such as magnetic permeability are defined exactly. So I presume it only makes sense to ask the question for constants that are not defined exactly.