Impact factor is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period.
Journal Citation Reports (JCR) ® is the only place where impact factors are reported. JCR® covers approximately 7,500 journal titles, which is only a small percentage of all journals in publication. Most journals do not have an impact factor. Access Web of Science from library portal & signin to access JCR.
The oldest and best known metric for measuring the impact of journals is the Journal Impact Factor (JIF or IF), determined by Clarivate's Journal Citation Reports. It is an average of the number of times articles published in a particular journal have been cited in the two previous years.
For example, if a journal has an impact factor of 15.84, this means that, on average, the articles published in this journal are cited approximately 16 times each in the two previous years:
Journal rankings are based on bibliometrics, a set of quantitative methods (1) to measure patterns of scientific publication and citation and (2) to assess the impact of research on the basis of citation activity. A list of top journals will differ, depending on citation tools, metrics chosen for analysis, and how broadly a field is defined. Journal rankings may change from year to year.
Not all journals are included in JCR, and the most appropriate journal for a piece of research may not necessarily have a high impact factor. Rating lists can provide useful insight into what might be desirable journals for article submission.