In summary, the developed protocol offers a robust and systematic approach for accurately determining the weight and length of Parhyale hawaiensis, an amphipod that is crucial for ecotoxicological research. By employing a Sartorius digital analytical scale with high precision and ImageJ software for weight and length measurements, respectively, this protocol ensures the reliability and consistency of data acquisition. The method highlights the importance of handling amphipods with care to minimise stress and maintain environmental stability throughout the procedure, thus reducing the likelihood of any potential harm to the organisms. Additionally, the protocol provides clear and concise step-by-step instructions, which facilitates the ease of replication and application in research settings. Overall, this protocol serves as a useful tool for scientists aiming to assess growth parameters and analyse the effects of environmental stressors on aquatic organisms, contributing to advancements in the field of aquatic ecotoxicology.