The role of sulfuric acid during atmospheric new particle formation is an ongoing topic of discussion. In this work, we provide quantitative experimental constraints for quantum chemically calculated evaporation rates for the smallest H2SO4-H2O clusters, characterizing the mechanism governing nucleation on a kinetic, single-molecule level. We compare experimental particle size distributions resulting from a highly supersaturated homogeneous H2SO4 gas phase with the results from kinetic simulations employing quantum chemically derived decomposition rates of electrically neutral H2SO4 molecular clusters up to the pentamer at a large range of relative humidities. By using high H2SO4 concentrations, we circumvent the uncertainties concerning contaminants and competing reactions present in studies at atmospheric conditions. We show good agreement between molecular simulation and experimental measurements and provide the first evaluation of theoretical predictions of the stabilization provided by water molecules.