To facilitate a better understanding of the role of self-control capacity in self-control processes, we examined its variation at intraindividual and interindividual levels, and positioned it in a nomological network with core affect. In two experience sampling studies, 286 university students reported their self-control capacity and core affect for a week. Results revealed larger person-to-person than day-to-day variation in self-control capacity, while its moment-to-moment variation could be weakly modeled as a diurnal pattern. Interindividually, participants with higher self-control capacity were happier and less stressed, but intraindividually higher self-control capacity was mainly associated with higher alertness and energetic arousal. Our results imply that self-control capacity is better conceptualized as a composition of interrelated sub-constructs rather than as a unified resource.