Michael Gusenbauer, “Google Scholar to overshadow them all? Comparing the sizes of 12 academic search engines and bibliographic databases”, Scientometrics, November 2018.
The findings provide first-time size estimates of ProQuest and EBSCOHost and indicate that Google Scholar’s size might have been underestimated so far by more than 50%. By our estimation Google Scholar, with 389 million records, is currently the most comprehensive academic search engine.
With the later proviso that there are likely to be many duplicates and near-duplicates, with such tools reporting…
the number of all indexed records on a database, not the number of unique records indexed. This means duplicates, incorrect links, or incorrectly indexed records are all included in the size metrics provided by ASEBDs.
As you can see, the article coins the ugly and unreadable “ASEBDs” for “academic search engines and bibliographic databases”. MASTs might be more mellifluous — Massive Academic Search Tools.