The purpose of this standard is to describe a gravimetric method for the determination of hygroscopic humidity, for the analysis of samples of natural or pretreated iron ores. The method is applicable to contents between 0.05% and 6%, and can be used when the analytical value of the constituent, calculated on a dry sample, is greater than 10%, in the following types of minerals: a) Pretreated minerals containing metallic iron (pre-reduced iron ores). b) Natural or pretreated minerals in which the S content is greater than 0.2%. c) Natural or pretreated minerals in which the water content is greater than 2.5%. The result obtained from the determination of hygroscopic humidity by means of this standard cannot be declared as part of the analysis of the mineral sample.