Provided is a protein quantitation standard having polypeptides of different molecular weights that functions as a mass quantitation standard in one lane of an electrophoretic gel. The protein quantitation standard includes unstained polypeptides having different electrophoretic mobilities that are present in different quantities, such that the bands in the gel have different intensities when visualized. The protein quantitation standard can also contain prestained polypeptides that function as visual molecular weight markers. Also provided are methods of determining the mass of a target polypeptide or protein using the protein quantitation standard.