Google Scholar Citations
From Wikipedia: The h-index measures both the productivity and impact of a scientist or scholar. A value for h of about 12 might be typical for advancement to tenure (associate professor) at major [US] research universities. A value of about 18 could mean a full professorship, 15–20 could mean a fellowship in the American Physical Society, and 45 or higher could mean membership in the United States National Academy of Sciences. According to Hirsch (who put forward the h-index), an h index of 20 is good, 40 is outstanding, and 60 is truly exceptional.