We examined the usefulness of five properties of gall size as alternative measures of true gall fitness, defined as the number of alates that emerged from a gall, in four species of Nipponaphidine galling aphids (Neothoracaphis yanonis, Metathoracaphis isensis, Monzenia globuli, and Dinipponaphis autumna). Among five properties (short diameter, long diameter, height, ellipsoidal volume, and ellipsoidal surface area), we determined that surface area was the most accurate and practical measure of gall fitness. This measure is particularly useful for obtaining a sufficient number of gall samples from reared species and species that experience high levels of predation. We also discuss other measures of gall fitness and various problems associated with them.