Q. What's the Journal Impact Factor?

The Journal Impact Factor is one way of comparing academic journals, based on the average number of citations they receive. It's one example of bibliometrics. 

The Impact Factor indicates the average (mean) number of citations for papers published in a journal over a 2 year period. As the average number of citations varies by academic field, it's not recommended for comparing journals from different disciplines (eg: biochemistry journals may have more citations on average than medical physics journals etc).

The best way to obtain the Impact Factor for a journal is to use Journal Citation Reports via Web of Science. Depending on what you want to measure/compare, it is worth exploring the other metrics available. Find out how.

Always remember that metrics like the impact factor can't tell you what the 'best' journal is. They're only a very broad measure of attention, not quality, and should always be used alongside qualitative judgements.

Guidance on how to use metrics to compare journals responsibly can be found on the University Metrics pages.