Following a historical review of methods that have been employed for measuring the interlamellar spacing of pearlite, these methods are compared with reference to a continuously cooled AISI 1040 carbon steel specimen. Extensiveana analysis using TEM thin foils and stereological analysis of TEM replicas, were conducted to determine the mean true spacing. Pearsall’s partial resolution method was rigorously controlled. The TEM method of searching for the finest pearlite colony as an estimate of the true spacing produces variable results with no fixed relationship to the mean true spacing. The analytical method of Roosz et al. for developing the distribution of true spacings produced reasonable agreement with the stereological estimate of the mean true spacing.