Protein precipitation by polyethylene glycol: A generalized model based on hydrodynamic radius

► Model based on PEG hydrodynamic radius corrects the errors of previous models which express PEG molecular weight explicitly. ► Predicts the effects of PEG shape, PEG size, protein size, environmental condition. ► Predictions agree reasonably well with independent solubility data. ► Selection of PEG precipitants should be based on its hydrodynamic radius, not molecular weight.