  The emergence of academic search engines (Google Scholar and Microsoft
Academic Search essentially) has revived and increased the interest in the size
of the academic web, since their aspiration is to index the entirety of current
academic knowledge. The search engine functionality and human search patterns
lead us to believe, sometimes, that what you see in the search engine's results
page is all that really exists. And, even when this is not true, we wonder
which information is missing and why. The main objective of this working paper
is to calculate the size of Google Scholar at present (May 2014). To do this,
we present, apply and discuss up to 4 empirical methods: Khabsa & Giles's
method, an estimate based on empirical data, and estimates based on direct
queries and absurd queries. The results, despite providing disparate values,
place the estimated size of Google Scholar in about 160 million documents.
However, the fact that all methods show great inconsistencies, limitations and
uncertainties, makes us wonder why Google does not simply provide this
information to the scientific community if the company really knows this
figure.
