Systems and methods for determining the composition of a drilling fluid using electro-rheology may be provided. A method for drilling a wellbore may include: circulating a drilling fluid in a wellbore; extending the wellbore into one or more subterranean formations; measuring impedance of at least a portion of the drilling fluid over time as one or more particulate additives in the drilling fluid settle; determining one or more model elements of an equivalent circuit model for modeling frequency responses of the drilling fluid from the impedance; and determining sag behavior of the drilling fluid based, at least partially, on the one or more model elements.