The Metabolic Theory of Ecology links the effects of temperature on metabolic rates at the cellular scale to large-scale ecological processes, providing a framework to predict how individuals, populations, and communities will respond to climate change. Metabolic Theory predicts that carrying shows a unimodal (hump-shaped) relationship with temperature, and that this hump will be flatter at low resource qualities. However, few studies have empirically tested this prediction, despite the importance of carrying capacity in understanding population persistence. To test the predicted effect of temperature on carrying capacity and to determine whether this is mediated by resource quality, we conducted a fully crossed experiment in which we grew populations of the model organism Tribolium castaneum for 22 weeks at all combinations of four temperatures (27.5 °C, 30 °C, 32.5 °C, and 35 °C) and three resource qualities (flour types). Our results support the predictions that carrying capacity follows a unimodal relationship with temperature and that it declines at lower resource qualities. However, we found no interactive effect of temperature and resource quality on carrying capacity. These findings support recent updates to theory describing temperature’s effect on carrying capacity, and contribute to our understanding of how population dynamics will shift under climate change.