The resources outlined on this page will assist in locating quantitative data for assessing journal quality. Note that such tools tend to be more useful for publications in natural and social sciences.
Journal impact factors change over time. They also differ greatly from one field to another. For example, Althouse and Bergstrom (2008) show that 2004 weighted impact factor for mathematics journals was 0.56; for molecular and cell biology it was eight times as high, 4.76.
Disciplinary differences in impact factors have to do with varied citation practices across fields, discipline-dependent lag times between publication and citation, as well as the discipline-specific number of citations an average article includes.
Althouse, B. M., West, J. D., Bergstrom, C. T., & Bergstrom, T. (2009). Differences in impact factor across fields and over time. Journal Of The American Society For Information Science & Technology, 60(1), 27-34.
SCOPUS provides access to peer-reviewed journal titles from international publishers in science, technology, social science and medicine. In the newest interface, an easy-to-miss "Compare Journals" link in the top right corner of the main search box will take you to a new journal comparison page. You will be able to enter up to 10 journal titles and compare them across several factors relating to the journal's quality including CiteScore, SJR, SNIP, as well as the number of citations.
Journal Citation Reports The number of articles published in journals indexed by the Web of Science and the number of citations to individual journals. This information may be viewed by journal name, subject, publisher, and country or territory. Be sure to choose science or social sciences before selecting a subject. For more information on how to use the database, see this University of Michigan guide or this tutorial.
Eigenfactor.org Free and searchable, this database covers the natural and social sciences and "lists newsprint, PhD theses, popular magazines and more." The Eigenfactor is also included in Journal Citation Reports (see above).
Pendlebury, D. (2009). The use and misuse of journal metrics and other citation indicators. Archivum Immunologiae et Therapiae Experimentalis, 57 (1), 1-11.