This International Standard specifies a method for determining the bound styrene content of emulsion-polymerized styrene-butadiene (SBR) rubbers by correlation with the measured refractive index of an extracted sample according to a table of refractive indices versus percentages by mass of styrene. The method is also applicable to extracted oil-extended emulsion-polymerized SBR as long as it produces a film suitable for refractive index measurements. It is not applicable to solution-polymerized SBR.