Body size, developmental rate, and metabolic rate were examined as potential phenotypic correlates of genome size using all 51 named species of Lepidoptera with recorded genome sizes. Genome sizes ranged 0.29–1.94 pg. Because no direct comparative measures were available, surrogates were used: wingspan for body size, voltinism for developmental rate, and grades of adult diel activity and adult feeding for metabolic rate. Analyses consisted of plotting genome size on surrogate values and fitting least-squares trend lines. At the order level, empirical - correlates of genome size with wingspan and voltinism were essentially null or flat. At family and subfamily levels, striking associations were found for wingspan and voltinism, but not for surrogates of metabolic rate, for which data were limited and surrogate validity uncertain. Geometrid species, nearly all of which were ennomiines, showed a sharp positive association between genome size and wingspan, Arctiidae a sharp negative association, and Noctuidae a flat association. Geometridae showed a sharp negative association between genome size and voltinism, Arctiide a sharp positive association, and Noctuidae a mild negative association. No phenotypic correlates of lepidopteran genome size were previously known. Suppositions were confirmed that phenotypic correlates are most likely to be detected at family and lower taxonomic levels.