When completing a citation analysis for a single article, it is important to use multiple tools because there is no single database that indexes all journal or all issues of a single journal title. As a result, different resources for citation counts have coverage gaps -- not all resources cover all subject matters thoroughly. In addition to coverage gaps, every database also differs in terms of format inclusion. Some include conference papers, books, dissertations and other works, while others do not.
Another consideration to bear in mind is there may be differences between resources as to author identity. Some databases or resources do not uniformly distinguish between authors with the same or similar names or pull together all publications by an authors who has published with name variations. If an author has not consistently published with the same name or exact spelling or format for his name, all of his work may not appear in a single search in Web of Science, for example, and his name may be listed differently in Google Scholar. This issue is known as "author disambiguation" and it it is a problem that tools like ORCID are targeted toward addressing. For more on this issue, see the Author Influence & Impact tab above.
Google Scholar includes multi-disciplinary journal articles, conference proceedings and books. Users can search for a particular work and then click on the Cited By (number) to see citation counts. Authors can also create a profile to track citations to their own articles and compute several citation metrics.
Word of caution - it is difficult to know which publications and dates are included in Google Scholar. Further, because of reported errors in its counts as a result of Google, inter alia, incorrectly identifying reviewers as authors and journal titles as article titles, results in Google Scholar should be carefully examined and should only be used as a supplement to other tools.
Web of Science is a subscription resource that includes journal articles (in Science Citation Index, Social Science Citation Index, and Arts & Humanities Index databases), conference proceedings (in Conference Proceedings Citation Index), and books (in Book Citation Index database)