Plasma-sprayed alumina coatings mainly consist of γ-alumina with minor amounts of α-alumina due to incorporation of incompletely fused powder. The presence of amorphous materials has also been mentioned in the literature, but not quantified. In this work, X-ray powder diffraction and Rietveld refinements were explored as potential tools for the determination of the amorphous content in plasma sprayed alumina coatings. To cross-check the accuracy of the Rietveld analysis, standard additions of amorphous alumina were performed. Both approaches provided consistent results supporting the validity of the Rietveld method for routine quantification of the amorphous phase in plasma-sprayed alumina. For the as-sprayed coatings studied in the present work, the amount of amorphous alumina was found to be 12.0 ± 0.7 wt.%.