Barn owls (Tytonidae: Tyto) have long been considered a single species, despite their worldwide distribution and despite being highly geographically variable in morphology. Multiple genomic studies have now demonstrated that the Common Barn Owl Tyto alba sensu lato complex has at least three deeply genetically diverged evolutionary units: Tyto alba sensu stricto, occurring from southern Scandinavia to South Africa; Tyto furcata, of southern Canada to Patagonia; and Tyto javanica, of the Himalayan plateau to Tasmania and the tropical Pacific. Their extensive geographic variation, however, greatly complicates delineation of their taxonomy. With the aim of shedding further light on barn owl taxonomy, we conducted a comprehensive morphological analysis of the three major Tyto alba s.l. clades, measuring up to 21 different morphometrics on 192 live and 1271 museum barn owl specimens. Our results clearly demonstrated mensural differences between the three evolutionary species units of barn owls, primarily in that the several subspecies of Tyto furcata as a clade are, sex-for-sex, considerably larger than the other two clades, especially in wing length. Despite Tyto javanica being sister to the other two clades and being somewhat intermediate in size, its several subspecies are more similar in overall size to subspecies of Tyto alba s.s. (the smallest-bodied clade) than either is to Tyto furcata. Our research supports and supplements the genetic and vocal evidence that recently led to the now widely adopted subdivision of the Barn Owl Tyto alba s.l. into three separate species.