There have been many attempts at measuring Māori identity and cultural engagement, yet there have been no scales created to specifically explore whanaungatanga. Whanaungatanga can be operationalised as active participation in and a sense of belonging to social groups and collective, reciprocal caring relationships. In this article, we document the development of a whanaungatanga scale alongside a measure of Māori identity. The research reported here analysed the responses of the rangatahi Māori who completed the Youth19 Rangatahi Smart Survey (Youth19, NMāori = 1,627), which was administered in secondary schools from the Te Tai Tokerau (Northland), Tāmaki Makaurau (Auckland), and Waikato regions in 2019. We discuss the deliberative parts of the scale development then move on to describe the factor analytic techniques employed, which identified a reliable three-factor structure for whanaungatanga, independent of the cultural identity questions in Youth19. We then show that the three subscales for whanaungatanga—with whānau, friends, and other adults, respectively—predict well-being for rangatahi Māori and can be used as a basis for further work.