Effective interactions are conveniently determined from experimental or numerical data by fitting a Debye–Hückel potential with an effective charge Z∗ and an effective electrolyte concentration c∗ as free parameters. In this contribution we numerically solved the Poisson–Boltzmann equation to obtain the so-called renormalised charge ZPBC∗. For sufficiently large bare charge Z one finds a saturation of Z∗ which scales as Z∗=Aa/λB, where a is the particle radius, λB the Bjerrum length and A a proportionality factor of order (8–10). The saturation value increases with increased total micro-ion concentration and shows a shallow minimum as a function of packing fraction. In addition, the bulk shear modulus G was measured along the melting line of a colloidal crystal to obtain ZG∗ and molecular dynamics simulations were performed within the primitive model for a pair of particles at different added salt concentration to obtain ZMD∗. ZPBC∗ was then used as reference for an extensive comparison to other effective charges as obtained in the present paper and taken from literature. We observe ZG∗ to be somewhat smaller than ZPBC∗ and other bulk experimental effective charges, while the simulation yields ZMD∗≈Z≫ZPBC∗. These differences are discussed in the light of charge renormalisation concepts and three and many body interactions.