Journal Impact Factors (JIF) are created from an analysis of the citation data in the Web of Science database. Theoretically, the higher the impact factor, the more prestigious the journal. Impact Factors are updated once a year in the Journal Citation Reports (JCR) database. 

The Impact Factor is calculated by dividing the number of citations to the journal in the JCR year, by the total number of articles published in the two previous years. An Impact Factor of 1.0 means that, on average, the articles published one or two years ago have been cited one time in the current JCR year. For example, a journal with a JIF of 1.0 in the 2015 JCR would have articles published in 2013 & 2014 that have been cited once in 2015. An Impact Factor of 2.5 means that, on average, the articles published in 2013 & 2014 were cited 2.5 times in 2015. Citing articles may be from the same journal, or from different journals.

There are some caveats that must be noted:

1. Only the ~11,000 sources in Science Citation Index (SCI) and Social Sciences Citation Index (SSCI) have JIF reported in JCR; journals in the Arts & Humanities Citation Index (AHCI), emerging sources, and conference papers do NOT receive JIF scores.
2. Citations come from all ~33,000 journals indexed by the complete Web of Science, not just from the SCI and SSCI journals.
3. Citations can be to any document type in the journal (i.e. citations could be to articles, news items, editorials, etc.)
4. The denominator contains only “citable items”, which are articles & reviews. Classification as an article or review is based on the section of the serial in which they are published. This generally excludes editorials, letters, news items, etc. from the denominator even though they are included in the numerator.

Step One

Go to the Journal Citation Reports database:

Step Two for individual titles

For a Single Title search, simply type in the full name of the journal into the search box and then select it from the results.  The impact factor is displayed on the journal profile page (you may have to browse down).

To see multiple years for the title, click the down arrow under "jcr year" (above the title) and select the year you want, or select "all years" to get 1997 to the current year.

Step Two for journal categories

For a Category (subject) search, try typing in the name of the category and selecting it from the "categories" list at the bottom of the results. To find an appropriate category, search for a journal first and notice its category in the 'journal information' section.  

The default sort is by impact factor.  You can change the sort (by clicking the column heading) to:

• Total Cites- the raw number of citations to the journal in the JCR year. 
• Impact Factor - the average number of times articles from the journal published in the past two years have been cited in the JCR year.

You can customize the indicators shown by clicking on the 'Customize' option in the top right. Other indicators often useful include:

• Article Influence - the average influence of a journal's articles over the first five years after publication.
• Immediacy Index - the average number of times an article is cited in the year it is published 
• Citable items - the total number of articles published in the journal in the JCR year.
• Cited Half Life - The median age of the articles that were cited in the JCR year. Half of a journal's cited articles were published more recently than the cited half-life.
• 5 year impact factor - the average number of times articles from the journal published in the past five years have been cited in the JCR year.
• Eigenfactor score - the number of times articles from the journal published in the past five years have been cited in the JCR year,with highly cited journals influencing the network more than lesser cited journals. Eigenfactor Scores are not influenced by journal self-citation.

You can also customize which year (1997 to the present) to view by selecting the 'filter' option to the left of the screen.

Note: Use the CLEAR button at the bottom of the left column to remove old searches from your session.

Eigenfactor and Article Influence scores are also available directly, for free, at Eigenfactor.org.

The Eigenfactor uses Thomson Reuters (ISI Web of Knowledge) citation data to compute EI and AI scores.

Eigenfactor Scores

A journal's Eigenfactor (EF) Score is a measure of the journal's importance to the scientific community.  Eigenfactor scores are scaled so that the sum of the Eigenfactor scores of all journals listed in Thomson's Journal Citation Reports (JCR) is 100.  In 2009, the journal Nature has the highest Eigenfactor score, with a score of 1.74605. The top thousand journals, as ranked by Eigenfactor score, all have Eigenfactor scores above 0.01.

Like the Impact Factor, the Eigenfactor Score is essentially a ratio of number of citations to total number of articles. However, unlike the Impact Factor, the Eigenfactor Score:

• Counts citations to journals in both the sciences and social sciences.
• Eliminates self-citations. Every reference from one article in a journal to another article from the same journal is discounted.
• Weights each reference according to a stochastic measure of the amount of time researchers spend reading the journal.

Article Influence scores

A journal's Article Influence (AI) score measures the average influence, per article, of the papers in a journal. As such, it is comparable to Thomson Scientific's widely-used Impact Factor. Article Influence scores are normalized so that the mean article in the entire Thomson Journal Citation Reports (JCR) database has an article influence of 1.00.

There are many other journal measures. An explanation of them is available here:

Walters, W. H. (2016). Information sources and indicators for the assessment of journal reputation and impact. The Reference Librarian, 57(1), 13-22. doi:10.1080/02763877.2015.1088426

Various journal measures can be found at the following sites: 

What are these metrics?

CiteScore:  is the average number of citations received by a journal in a calendar year divided by all items published in that journal in the preceding three years. 

Teixeira da Silva, Jaime A, & Memon, A. R. (2017). CiteScore: A cite for sore eyes, or a valuable, transparent metric? Scientometrics, 111(1), 553-556. 

SNIP: Source Normalized Impact per Paper is defined as the ratio of a journal’s citation count per paper and the citation potential in its subject field.2 It compares directly to Web of Knowledge’s Impact Factor. SJR is based on times cited, but also uses an algorithm similar to Google’s PageRank to calculate article influence, which it uses to create rankings; it accounts for both the number of citations received by a journal and the prestige of the journals where such citations originated.  Users can compare rankings of up to ten journals at a time and display top journals.

H Moed.  "Measuring contextual citation impact of scientific journals."  Journal of Informetrics 4 (3): 265-277; July 2010. doi:  10.1016/j.joi.2010.01.002

SJR: SCImago Journal Rank indicates the influence of the average article from the journal. It is a measure of scientific influence of scholarly journals that accounts for both the number of citations received by a journal and the importance or prestige of the journals where such citations come from.1 With SJR, the subject field, quality and reputation of the journal have a direct effect on the value of a citation.

Borja González-Pereira, Vicente P. Guerrero-Bote, Félix Moya-Anegón. "A new approach to the metric of journals’ scientific prestige: The SJR indicator" Journal of Informetrics  4 (3): 379-391; July 2010. doi: 10.1016/j.joi.2010.03.002.

IPP: Impact Per Publication is the number of citations given in the present year to publications in the past three years divided by the total number of publications in the past three years