The purpose of this study was to examine social workers’ perceptions of safe staffing levels and correlate these perceptions with standardised measurements of well-being in the UK. This cross-sectional mixed-methods study analysed data from 406 social workers from November 2022 until late January 2023. Data were collected using anonymous online surveys including both qualitative and quantitative methods examining mental well-being, burnout and intentions to leave the profession post-coronavirus disease 2019. Findings revealed that only one-third of social workers responding perceived that they work in an environment of safe staffing. There were also significant differences in well-being and an increase in personal, work-related and client-related burnout in social workers who believed their service did not operate a safe staff-to-service user ratio. Likewise, compared to those who perceived their service to operate within a safe staff-to-service-user ratio, those who perceived unsafe ratios were more likely to communicate their intention to leave the profession. Qualitative findings helped contextualise the quantitative results. These findings suggest that increased demand for social work services, shortage of qualified social workers, high workloads, inadequate resources and retention problems, contribute to additional pressure on existing staff and have implications for policy, practice and research in social work.