Despite citation counts from Google Scholar (GS), Web of Science (WoS), and Scopus being
widely consulted by researchers and sometimes used in research evaluations, there is no recent
or systematic evidence about the differences between them. In response, this paper investigates
2,448,055 citations to 2,299 English-language highly-cited documents from 252 GS subject categories published in 2006, comparing GS, the WoS Core Collection, and Scopus