Work out journal impact factor instantly with clear inputs, formula shown and shareable results.
The journal impact factor divides this year's citations to the previous two years' articles by the number of those articles. 4200 citations to 650 items gives 6.46. It is a journal-level average dominated by a few highly cited papers, so it says very little about any individual article - the core objection behind the DORA declaration.
Impact factor
JIF = citations this year to the last two years / citable items in those two years
Window
a two-year citation window is the standard definition
Because citation distributions are highly skewed, so the mean misrepresents typical articles. DORA urges against using it to judge individual researchers.
Research articles and reviews, but not editorials or letters - which is why the denominator can be negotiated and the metric gamed.