Introduction. Pressed by the increasing social importance of digital information, including the current attention given to the ‘big data paradigm’, several research projects have taken up the challenge to quantify the amount of technologically mediated information. Method. This meta-study reviews the eight most important inventories in a descriptive and comparative manner, focusing on methodological differences and challenges. Results. It shows that approaches differ in terms of scope and research focus. This leads to different answers to the question of ‘how much information?’. Differences include how the information realm is conceptualised (e.g., in terms of stocks or flows, or in terms of creation or consumption, etc.); differences in the unit of measurement (words, bits, minutes, etc.); varying geographic and temporal scopes; and diverse additional attributes that highlight complementary aspects of the amount of information (e.g., the kind of technology, the sort of content, the type of user sector, etc.). Conclusion. The study reveals how different answers to the ‘How much information?’ question hinges upon the particular question on the researchers’ mind and on the subsequent methodological choices. Differences in findings stem from different research interests. The review ends with a discussion of the remaining theoretical and practical challenges.