In a similar way to the simulations, in a second step, we fit the experimental data by adjusting the reference volume via a 0 and the microgel maximum charge Z max,a for the system containing the lowest salt concentration c res salt = 0.001 M. In Fig. , we present the swelling ratio, v/v max , in terms of the ratio of the microgel equilibrium volume over the largest swelling volume, versus pH sys . The blue solid line represents the theoretical prediction for fitting parameters a 0 = 4σ and Z max,a = 850. We see that the theoretical prediction adequately captures the behavior of the experimental measurements. The fitting reflects the fact that the effective number of charges relevant to the swelling model is smaller by approximately 8 orders of magnitude than the chemically available ionizable groups, within the Poisson-Boltzmann scheme. The consequent net charges are in the order of Z net ≈ 200. This is consistent with the measurements of net charges via scattering, where they find several orders of magnitude differences between the titration measurements and the scattering charge.