How is an h-index calculated?
see also "How can I get my h-index"
Answer
H-Index can be calculated using any group of articles. The result varies based on the number of items with citations and the citation source used.
Calculation
H-index counts the number of publications for which an author has a citation count that matches is or greater than the number of articles. Or, as Google Scholar describes it: "The largest number h such that h publications have at least h citations."
For example, an h-index of 17 means that the scientist has published 17 papers that have each been cited at least 17 times.
If the scientist's 18th most-cited publication was cited only 10 times, the h-index would remain at 17. If the scientist's 18th most-cited publication was cited 18 or more times, the h-index would rise to 18.
In some places, like Scopus, there is an option to exclude self-citation.
Different Sources = Different Results!
IMPORTANT! Different databases give different h-index values.
Each database can only calculate the h-index based on the citations it contains. Since databases cover different publications in different ranges of years, the h-index result can be expected to vary. Both Scopus and Web of Science are considered reliable sources, yet, the citation count in Web of Science is usually different the citation count in Scopus due to unique journal titles indexed in each database.
Also, no single external database will include every one of your articles. The only place where you have complete control of your publications list is the Weizmann Research Publications Database.
What is considered a "good" h-index may differ depending on the scientific discipline. A number that is considered low in one field might be considered quite high in another field.