Aim: Emergency nurses work in an environment of high cognitive mental workload. Excessive cognitive mental workload may result in patient harm and nurses' burnout. Therefore, it is necessary to understand nurses' subjective experience of cognitive workload. This scoping review aimed to curate literature about the subjective experience of cognitive mental workload reported by nurses and psychometric measures of the phenomenon.Design: The scoping review was conducted in accordance with JBI methodology and reported using PRISMA extension for scoping review checklist.Methods: A priori protocol was created with Peer Review of Electronic Search Strategies checklist and registered in the OSF registry. Databases including PubMed, CINAHL, ProQuest, Scopus, Science Direct, Web of Science and Google Scholar were searched. Published reports were reviewed against the eligibility criteria by performing Title and Abstract screening, followed by Full‐text screening. The initial search yielded 1373 studies. Of these, 57 studies met the criteria for inclusion in this study.Results: The search revealed five general measures of cognitive mental workload and their variations. Only one customised measure specifically for medical–surgical nurses was found in the study. Identified measures were collated and categorised into a framework for conceptual clarity. NASA Task Load Index and its variations were the most popular subjective measure of cognitive mental workload in nursing. However, no measure or self‐report scale customised for emergency nurses was identified.Patient or Public Contribution: The findings of this scoping review can inform future research into the cognitive mental workload of nurses. The findings have implications for workplace health and safety for nurses and patients.