Macroecological patterns of life history traits, such as larval size, are fundamental to understanding the biogeography and diversity of marine invertebrates. The present dataset provides curated information on carapace length (CL) of the first larval instar of decapod crustaceans. Data were obtained from published descriptions in which the morphology of the larva was illustrated using drawings or photographs. We extracted the CL data measuring from the anterior margin (or the base of the rostral spine when present) to the posterior dorsal margin of the carapace. We used our own collection of published taxonomic descriptions to gather data regarding "number of larval stages" and "size of the first larval instar". To expand the dataset, published information was added from the Institute for Scientific Information Web of Knowledge using the search terms "larva" AND "development" AND "Decapoda" AND "description". Moreover, taxonomic journals (e.g. Zootaxa, Crustaceana, Journal of Crustacean Biology, etc.) were individually searched for extra datasets. We were careful to include only studies following the taxonomic standard propositions by Clark et al. (1998) updated by Clark and Cuesta (2015). To avoid misidentifications, we only used descriptions based on larvae obtained from laboratory-reared ovigerous decapods or collected in the field and identified by DNA barcoding. Moreover, those descriptions with low quality drawings/photographs, and/or without scale were discarded. Following these criteria, we screened the abstracts and figures to select appropriate studies. In some cases, we extracted carapace size data directly from published tables or scatter plots using the free online app PlotDigitalizer (https://plotdigitizer.com). Our dataset of larval size includes a total of 645 species across Decapoda: 47 Achelata, 135 Anomura, 8 Astacidea, 13 Axiidea, 292 Brachyura, 113 Caridea, 20 Dendrobranchiata, 11 Gebiidea, 1 Polychelidea, 3 Stenopodidea. Species names and phylogenetic position of all decapods were updated using the World List of Decapoda (DecaNet eds., 2024). In addition to CL, we gathered data on the feeding mode (lecithotrophic or planktotrophic) of the first larval instar, and number of stages required to complete the larval phase, when the information was available.