For carbon analysis in an iron-matrix the C-Kα intensity is not only a function of the amount of graphite. but also of the diameter of the spherolites and, for a given total carbon content, of the graphite/cementite ratio. In order to verify this, steel and caststeel sample surfaces were photographed before and after etching and the images digitized. The arcal fractions covered by graphite, cementite, and iron were used to compute the corresponding individual weight fractions and total carbon contents. Count rates were drawn to the scale of these as well as of the nominal carbon concentrations.