To measure individual differences in working memory capacity, complex span tasks have been developed. These tasks, which predict several aspects of higher-order cognition, have associated ranges of storage item sizes that are regularly controlled to avoid ceiling and floor effects in performance distributions. To examine the memory load incurred by the ranges of storage item sizes, this study used different storage item sizes for complex span tasks across verbal, numerical, and spatial content domains. Particularly examined were the relations among processing, storage, and general fluid abilities of the different storage item sizes of complex span tasks. Results of latent-variable analysis indicate different relations among these components of participants’ performances in complex span tasks, for which the item sizes differed. The influences on the memory load of storage item sizes of these tasks are discussed.