Journal metrics attempt to quantify the quality or influence of a given journal for purposes of comparison.
These metrics describe the journal as a whole, not individual articles.
Important factors to consider are the time frame of the calculation and whether or not the metric includes all items in a journal (e.g. letters or news) or just the "citable" items. Measures that include all items tend to penalize journals that publish a variety of document types
The Journal Impact Factor, also known as Impact Factor, is the oldest and most widely used measure. Its use is often criticized for having a too-short window for analysis (two years) and failure to recognize differing expectations of citation rates among disciplines.
Impact Factor is similar to the CiteScore but uses Web of Science to gather its data and two years rather than three as the publication period.
A journal's CiteScore is the total number of citations in a year to articles published in the three previous years, divided by the total number of articles published in those three years.
CiteScore is limited to only scholarly articles, conference papers and review articles and does not consider citations from trade publications, newspapers, or books.
CiteScore is similar to the Impact Factor but uses Scopus to gather its data and three years rather than two as the publication period.
A journal’s Eigenfactor Score counts the citations made to a journal over time, but gives more weight to the citations from highly ranked journals than lower ranked ones.
Eigenfactor ranks the overall impact of a journal, and not the impact of articles within that journal.
A free website, based on materials within Scopus.
The rankings seek to measure the prestige of a journal while accounting for both the number of citations recieved by the journal and the prestige of the journals from which the citations come. Full documentation is available on their website.
Source Normalized Impact per Paper (SNIP) measures the average citation impact of the publications of a journal. It seeks to correct for differences in citation practices between scientific fields, thereby allowing for more accurate between-field comparisons of citation impact.