A warning: Impact metrics are controversial and do not necessarily give an accurate picture of the impact or usefulness of a particular journal or the research output of a particular scholar.
Journal impact metrics measure the importance of a journal in a particular field relative to other journals in the same field. There are several different metrics employed to measure this relative importance. Three tools are covered in this guide:
Access Journal Citation Reports
From the publisher: Journal Citation Reports® is a comprehensive and unique resource that allows you to evaluate and compare journals using citation data drawn from over 11,000 scholarly and technical journals from more than 3,300 publishers in over 80 countries. It is the only source of citation data on journals, and includes virtually all areas of science, technology, and social sciences. Journal Citation Reports can show you the:
Citation and article counts are important indicators of how frequently current researchers are using individual journals. By tabulating and aggregating citation and article counts, JCR offers a unique perspective for journal evaluation and comparison.
Watch Web of Science's training videos for guidance on the various ways to use Journal Citation Reports.
Eigenfactor purports to provide two metrics (from the publisher):
From the publisher:
Publish or Perish is a software program that retrieves and analyzes academic citations. It usesGoogle Scholar to obtain the raw citations, then analyzes these and presents the following statistics:
Web of Science can generate citation reports on a variety of indicators for a group of papers or a particular author. This video outlines the several tools built into Web of Science for analyzing citation data.