The Keplerate-type polyoxometalates (POMs) are known to self-assemble as single-layered hollow shells. It has been regarded that only when POMs carry moderate amount of charges, shells are observed in experiments. Using a coarse-grained molecular model for POMs and invoking patchy hydrogen bonding attractions, we show from Simulated Annealing simulations that patchy attraction alone is sufficient to stabilize sheet-like structure, which is the precursor for the formation of shells. The electrostatic interactions may play a role only in the folding of the sheet-like structure into a spherical shell. Simulation results suggest that shells can be formed even at low charge density. We report a theoretical model to predict the radius of the shell (R∗) formed by weakly charged POMs in the limit of constant charge density. The model predicts that R∗ scales with (i) dielectric constant of the solution (ε) as and (ii) with charge density (σ) as . This behavior is qualitatively different from the highly charged limit that is often encountered in these systems. Using the model, we find that the radius of the shell (20–120 nm) generally observed in experiments corresponds to charge densities in the range of 10−3–10−2 nm−2, and the number of charges per POM in the range of 0.02–0.2.