This explanation from Andre Spicer at The Conversation (via Publishing Cambridge) tells you how to calculate your H-index score.

For most of us this is a somewhat arcane matter — academics however are always concerned to know (and have others know) just how important their research is. It used to be that an author was ranked by the number of citations to their research papers and books that there were. This potentially leads to the distortion that one paper frequently referenced can make a professor look influential beyond all reality. The H-index is a ranking based on numbers of papers referenced and number of times referenced. Thus Mr Spicer tells us his H score is 28 because 28 or his papers have been referenced at least 28 times.