Social impact measurement has remained a challenge for both social enterprises (SEs) and scholars in the SE field. Despite increased scholarly attention given to SE social impact and its measurement in recent years, scholars continue to call for more research to advance the approaches for measuring social impact in SEs. This study aims to provide a reliable and valid social impact scale for SEs, which can be used as an alternative or a complementary scale to existing quantitative social impact tools. Through a systematic scale development process, it develops a 31-item multidimensional social impact scale based on the triple bottom line sustainability framework and using perception-based or constituency-based feedback. Data analysis confirms the reliability and validity of the scale across two studies involving different SE samples and country contexts. The study also discusses implications for theory and practice and recommendations for future research.