What Sites and Databases Does Turnitin Check Against?
Turnitin's similarity score is only as broad as its index. Knowing what is in that index tells you exactly where your risk is — and where a free checker will give you false comfort.
The open web
Turnitin maintains its own crawl of tens of billions of current and archived web pages: Wikipedia, blogs, news, course sites, essay mills, forums, and open-access repositories. Archived pages matter — deleting a source after copying it does not help.
Previously submitted student papers
Over 1.9 billion papers submitted through Turnitin worldwide. This is the database no free checker can reach, and it is where most surprise matches come from — including your own earlier work if it was stored.
Academic publications
Content licensed from major publishers and databases including Crossref members, ProQuest dissertations, IEEE, Springer, Wiley, Taylor & Francis and similar. Paywalled journal articles are covered even though a Google search would not surface the full text.
What Turnitin cannot see
Private university intranets it has no licence for, paywalled content outside its publisher agreements, printed books that were never digitised into its index, and papers submitted elsewhere as non-repository. Translated text is also weakly covered — Turnitin has a translated matching feature, but it is far less reliable than same-language matching.
Why this changes how you check
A free web checker covers roughly the first category and nothing else. If your matches come from a classmate's old assignment or a paywalled paper, only a genuine Turnitin run will show them.
FAQ
Does Turnitin check books?
Only books digitised into its licensed publisher content. Many printed-only books are not covered.
Does Turnitin check other students' papers from other universities?
Yes. The student paper database is global, not per-institution.
Need an official Turnitin report?
Order a real Turnitin similarity or AI detection PDF report from $1. Non-repository, delivered in minutes on WhatsApp or Telegram.
Related reads
Is 15% a good Turnitin score? What about 25%? Here is what similarity percentages actually mean and what most universities accept.
The ten most common Turnitin mistakes that get students in trouble — from accidental self-plagiarism to submitting to the wrong repository setting.
What does non-repository mean in Turnitin, and why does it matter for your final submission? Plain explanation with real examples.