Body size is a fundamental functional trait that integrates various morphological and physiological characteristics, which respond differently to environmental pressures. When expressed as body mass, body size provides insights into energy flows, scaling up from individual to ecosystem levels using the integrative theoretical approach of the Metabolic Theory of Ecology (MTE; Brown et al., 2004).

According to MTE, individual body mass is a convenient proxy of individual energetics, space use foraging behaviour, population density and energy use, ecosystem processes and services.

On the other hand, assessing individual body mass is problematic for many groups of organisms, being the individuals either too small or too large for practical measurements or the whole methodological process too time consuming and expensive.

Length-weight relationships offer a convenient means of estimating individual body mass from simple measurements of individual length.

To this aim, we have assembled an extensive length per weight database, continuously growing with increasing international collaborations, of 7500 animal species, mainly covering invertebrate and fish species. At higher taxonomical level we have collected length per weight relationships of 133 animal orders, corresponding to more than the 15% of the animal orders.

Here, we present an e-service developed by LifeWatch Italy to allow researchers to estimate individual body mass of the taxa pertaining to the already available orders from the respective length per weight relationships.

The database's weight-length relationships are set to be expanded through an intensifying international collaboration, with the aim of implementing the service at more specific taxonomic levels. The proposed model efficiently obtains biomass data useful for functional community analyses, ecological assessments, and environmental monitoring.

This approach helps to bridge the gap in the provision of high-resolution, quantitative data by providing a pragmatic, transferable tool for ecological studies in both terrestrial and aquatic ecosystems.