Citation impact provides a measure based on the number of citations of scholarly works in other scholarly publications. Citation metrics are usually calculated at article level, but they can also be used to calculate author and journal impact metrics.
Search a range of databases that provide citation counts since Web of Science and Scopus do not cover all disciplines well. There are a number of databases that can help you to count citations. However, they will not provide tools to analyse citations.
Keep track of your process of counting citations. For example, record the databases you used, and whether you included or removed self-citations.
In Web of Science use the name of the first author of an article since secondary authors are not always found in the Cited Reference searches.
No citation tool will provide a complete citation count. Variations occur because citation tools have different source materials, date ranges and sometimes erroneous records.
See below an example of distribution of citations of a book in Bar-Ilan, J. (2010) Citations to the “Introduction to informetrics” indexed by WOS, Scopus and Google Scholar. Scientometrics, 82(3), p.504.
Note also that citation counts are not comparable across disciplines. For example, citation counts in Social Sciences and Humanities are lower because researchers are more often publishing in books and conference papers that are not well covered by citation databases.