Sci-Hub, which allows users to access articles that are behind paywalls, was created in 2011 and has grown rapidly since.
PeerJ says that, until now, the extent of Sci-Hub’s coverage was unclear.
Out of the 69 percent, the coverage varied by area with 92.8 percent of articles in chemistry journals compared to 76.3 percent for computer science.
The website also offers 77 percent of the 5.2 million articles published by inactive journal.
PeerJ said that Sci-Hub provided access to 99.3 percent of valid incoming requests, proving that the subscription publishing model was becoming unsustainable.
More than 97 percent of articles published by Elsevier were available on the site.
Earlier this year, Elsevier was granted $15 million in damages from its copyright infringement lawsuit against Sci-Hub and the Library Genesis project.
The US District Court for the Southern District of New York found the defendants guilty on 21 June of wilfully infringing Elsevier’s copyright behind various scholarly articles.
The court calculated the award based on a representative sample of 100 infringed works and has forced US domain registries to suspend the defendant’s domain names.