Listeners associate low voice pitch (fundamental frequency and/or harmonics) and formants (vocal-tract resonances) with large body size. Although formants reliably predict size within sexes, pitch does not reliably predict size in groups of same-sex adults. Voice pitch has therefore long been hypothesized to confound within-sex size assessment. Here we performed a knockout test of this hypothesis using whispered and 3-formant sine-wave speech devoid of pitch. Listeners estimated the relative size of men with above-chance accuracy from voiced, whispered, and sine-wave speech. Critically, although men's pitch and physical height were unrelated, the accuracy of listeners' size assessments increased in the presence rather than absence of pitch. Size assessments based on relatively low pitch yielded particularly high accuracy (70%-80%). Results of Experiment 2 revealed that amplitude, noise, and signal degradation of unvoiced speech could not explain this effect; listeners readily perceived formant shifts in manipulated whispered speech. Rather, in Experiment 3, we show that the denser harmonic spectrum provided by low pitch allowed for better resolution of formants, aiding formant-based size assessment. These findings demonstrate that pitch does not confuse body size assessment as has been previously suggested, but instead facilitates accurate size assessment by providing a carrier signal for vocal-tract resonances.