We calculated the dimensionless gyromagnetic ratio ("g-factor") of self-gravitating, uniformly rotating disks of dust with a constant specific charge . These disk solutions to the Einstein-Maxwell equations depend on and a "relativity parameter" γ (0 < γ ≤ 1) up to a scaling parameter. Accordingly, the g-factor is a function g = g(γ, ). The Newtonian limit is characterized by γ 1, whereas γ → 1 leads to a black-hole limit. The g-factor, for all , approaches the values g = 1 as γ → 0 and g = 2 as γ → 1.