Limited capacity for visual perception results in various “inattentional blindness” phenomena across a wide variety of manipulations that load perception. Here, we propose that these phenomena are mediated by an underlying generalized capacity for visual perception, which also underlies subitizing: the ability to enumerate a limited number of items in parallel from a brief exposure. We tested this proposal by examining whether individual differences reveal common intraindividual variance between measures of visual perception as well as of subitizing capacity. Visual perception was measured in change blindness (Rensink, O’Regan, & Clark, 1997), load-induced blindness (Macdonald & Lavie, 2008), and multiple object tracking tasks. Subitizing capacity was measured as the number of items that could be reported in parallel in an enumeration task. Perceptual capacity as indexed by subitizing was consistently a unique predictor of performance in change blindness, load-induced blindness, and motion tracking beyond any general factors that apply to both subitizing and estimation of larger set sizes. Moreover, when measures of working memory were included, factor analysis indicated two orthogonal factors: perceptual and working memory. Overall, the results support the hypothesis of a generalized capacity for visual perception, and establish subitizing capacity as a predictor of individual susceptibility to inattentional blindness under load.