Scopus uses CiteScore to measure journal impact. CiteScore measures the average number of citations received per document published in the journal. Scopus also keeps a running tally of current year citations to predict the journal's future CiteScore.
2019 CiteScore and 2020 CiteScore Tracker for Nature
SCImago Journal Rank measures the weighted citations received by the journal. Citation weighting depends on the subject field and prestige (SJR) of the citing journal.
Source Normalized Impact per Paper (SNIP) measures the actual citations received relative to the citations expected for the journal’s subject field.