Whether voice formants provide reliable cues to adult body size has been contested recently for some animals and humans and the outcome bears critically on theories of social competition and mate choice, language origins, and speaker normalization. We report two experiments to test listeners’ ability to assess speaker body size. In Experiment 1, listeners heard paired comparisons of the same short phrase spoken by two adults of the same sex paired randomly with respect to height and indicated which was larger. Both sexes (M=20; F=22) showed an equal but modest ability to identify the larger male (mean correct=58.5%; T=31.5, P<0.001) that correlated with the magnitude of their height difference but could not pick the larger female (mean correct=52.0%; T=1.05, P=0.305) regardless of the height difference. Experiment 2 used single word comparisons, focused only on male voices, and controlled F0 while manipulating F1−F4 between speakers. When F0 was equal but F1−F4 predicted the height difference between speakers, both sexes (M=12; F=18) correctly chose the taller male (80%). When F1−F4 values of the shorter male were reduced below those of the taller male (or vice versa), subjects shifted to pick the shorter male as being larger.