<p>Morphometric relationships are fundamental in biological and fisheries sciences, particularly for species of high commercial value such as spiny lobsters (<i>Panulirus</i> spp.). This study presents a comprehensive and systematic review of length-length (LLR) and length-weight (LWR) relationships for <i>P. meripurpuratus</i>, <i>P. laevicauda</i>, and <i>P. echinatus</i> captured along the Brazilian coast. In addition, we also show graphically the morphometric index reported from previous studies. A total of thirteen LLR and nine LWR studies published between 1963 and 2025 were selected following PRISMA 2020 guidelines. Morphometric indices and regression equations were analyzed by sex and region. In general, males exhibited proportionally larger and heavier carapace and females present smaller and heavier abdomen, possibly reflecting sex-specific functional adaptations. Although average ratios of one-third for carapace length and two-thirds for abdomen length (AL) are frequently cited, our results show that these proportions are not stable across body sizes or sexes. Males, especially larger individuals, tend to deviate more from this pattern probably influenced by potential ecological or reproductive advantages of a large carapace. Moreover, the AL displayed greater variability as an explanatory variable, potentially influenced by morphological plasticity. Given the large number of studies reporting equations based on different body measurements, we highlighted the most recommended equations following five criteria to guide future research and applications involving LLR and LWR. These equations aim to provide a more consistent basis for comparative analyses and fisheries assessments. We list desired protocols to achieve consistency between studies, particularly for AL, and urge researchers to report regression parameters and conditions under which measurements were obtained. We also call for future studies to investigate the effects of freezing and tail positioning on morphometric accuracy.</p>