As you may know, the Web of Science (WoS) resource enables you to get impact factors for journals as well as citation reports (incl. citation counts and h-indexes) for particular authors. But I’ve just been looking at a program called Publish or Perish which analyses results from Google Scholar to also provide citation counts, h-indexes and so on. It therefore allows you to compare any citation analyses you obtain from WoS.
The Publish or Perish program is free (and quick) to download from here.
I just did a quick search in both WoS and Publish or Perish. For the work this academic had published from 2000 onwards his h-index in WoS was 7 and in Publish or Perish it was 9. But after looking at the results in Publish or Perish I found 5 duplicates. After deleting these, the h-index reduced to 8. So Publish or Perish seems to compare well with the results from WoS.
It’s useful to bear in mind that WoS only indexes journal articles and proceedings so there maybe books an author has written which don’t appear in a WoS citation analysis. Google Scholar, on the other hand, indexes books as well as journals and proceedings – but its content does lack some important sources that are available in WoS. It also appears that it does not index older material available on WoS.