This International Standard describes a test method for the determination of the mean crystallite height of a representative, pulverized sample of calcined petroleum coke by interpretation of an X-ray diffraction pattern produced through conventional X-ray scanning techniques. It applies to carbonaceous materials used in the production of aluminium. Calcined petroleum coke contains crystallites of different heights. This test method covers the determination of the average height of all crystallites in the sample by empirical interpretation of the X-ray diffraction pattern. The crystallite diameter (La) is not determined by this test method.