<p>Formants are a basic component of primate vocalizations, crucial for acoustic transmission and auditory perception of orofacial gestures for communication. Unfortunately, the estimation of formant frequencies is tricky and has resulted in flawed analyses in the literature. We propose theoretical guidelines and a procedure for performing appropriate analysis and avoiding faulty formant measurements. First, we show that a vocalization’s first four resonance frequencies, formants F1 through F4, must fall within a “Maximal Acoustic Space” (MAS) that can be determined from a prior estimate of the vocal tract length (VTL) of the target primate species, group, or individual. We provide MAS configurations for VTLs corresponding to a range of primate species, together with a set of known VTL estimates for available species. Second, we present simulations showing that high values of the fundamental frequency, f0, can be mistaken for formants, and we propose a rule of thumb for discarding erroneous measurements related to confusions between formants and f0 harmonics. We then describe a protocol whereby researchers can gather priors on VTLs and MASes to frame their study’s possible formant values, evaluate formants by checking that they fall within that MAS and are not f0 harmonics, reevaluate VTLs from formant results, and finally normalize formant frequencies by VTL to validly compare results between species, groups, or subjects, or with human speech. This analysis framework should increase the reliability of formant estimates and contribute to trustworthy analysis of primate vocalizations.</p>