Use Journal Citation Reports to calculate the impact factor of more than 7,500 academic journals.
To perform a search for citation reports from a specific journal, visit Journal Citation Reports and type the journal title you wish to search for.
You will be presented with a summary for that journal, including citations, impact factor, 5 year impact factor, amongst other metrics.
Journal Impact Factors can be questioned due to:
An anglo-american linguistic bias
Field dependency – only citations within the same academic field are considered in calculation
Articles gaining prestige from higher recognized journals contributing to a “Matthew effect” – popular journals are read more frequently and are more frequently cited. Their articles being more frequently read – a vicious circle which means that prestigious journals obtain a greater following at the expense of smaller ones
Other articles using incorrect or incomplete citations not being added to the citation count
Data manipulation – articles published at the beginning of the year have a longer time period in which to be read and or cited than those published later on in the year. As only the calendar year is used in calculation, this bias is not represented in calculation
For more details, see this article from the KTH Royal Institute of Technology