The Complex Span paradigm is one of the most influential and widely used instruments for measuring working memory capacity (WMC). We report the results of four experiments designed to explore the feasibility of obtaining valid estimates of WMC online. We explored the relationships between the Complex Span tasks and fluid intelligence (gF) in the lab and on the web using a new platform called the Online Working Memory Lab (the OWL). The OWL is universally accessible across all computer operating systems and functions in both local and remote contexts, allowing researchers to sample more diverse subjects from practically anywhere. Experiments 1 and 2 showed that the Complex Span failed to predict gF when the to-be-remembered stimuli were letters and the tests were taken online. We increased the predictive validity of the test battery in Experiments 3 and 4 by replacing the letters with memory stimuli that were more difficult to write down in an unproctored setting. This work describes our most recent attempts to measure working memory capacity in the wild.