Citation counts measure the impact of an author by counting the number of times they are cited in another work. There are different ways to calculate this.
The h-index measures both the productivity (number of articles published) and the impact (number of citations received) of a researcher or scholar. The h-index indicates the number of publications n that were cited at least n times. The index can also be applied to the productivity and impact of a scholarly journal as well as a group of scientists, such as a department or university.
If you have published 5 articles and each article has been cited at least 5 times, your h-index is 5.
Like most bibliometrics, the h-index is discipline specific, and average h-indexes vary widely from one subject area to another. Comparisons should not be made across disciplines or subject areas. The h-index also discriminates against early career researchers who have not yet published as many articles or whose articles have not yet been available long enough to have been read and cited by others.
Bibliometric databases that count citations include Web of Science, Scopus, Google Scholar, and some subject specific databases such as MathSciNet and SciFinder. It is important to note that these databases index different lists of journals, thus their derived h-indexes may vary. Citations in sources (journals, books, newspapers, etc.) not indexed by WOS, Scopus, or Google Scholar are not counted towards an author’s h-index.
The g-index is a variant of the h-index, which takes into account the citation evolution of the most cited papers over time. It can be determined by listing publications in decreasing order of number of citations. The g-index is the unique largest number such that the top g articles together received at least g squared citations. A g index of 5 indicates that the top 5 papers have a cumulative citation total of 25. A g-index of 6 would mean that your top 6 publications have been cited 36 times.
The m-quotient is another variation of the h-index; it aims at weighing the period of academic endeavor so that even junior scientists attain the importance that they deserve. The m-quotient is derived by dividing the h-index by the number of years since the first publication.
The i10-index is a Google Scholar metric. It indicates the number of academic publications an author has written that have been cited by at least ten sources.
The following factors provide additional evidence of research impact and might be relevant for competitive grant applications and academic promotions: