H-index can be found from databases like Web of Science and Scopus or from Publish or Perish software program. Publish or Perish is a free software program for analyzing Google Scholar citations.
In order to calculate researcher’s H-index accurately one need to take into account only those publication that really belongs to that particular researcher and same time try to find all the relevant publications from the database. Therefore, to calculate H-index accurately it is necessary to have researcher’s updated list of publications as a reference.
Check that all author’s publications with impact factor are included in the search results. You can save retrieved publications to Marked List (Web of Science) or to My List (Scopus). When you have found all the relevant publications from the database, choose Create citation report (Web of Science) or View citation overview (Scopus). From citation report/citation overview you can find H-index, total amount of citations, citations per each year and citations per each publications.