Hirsch: A scientist has index h if h of his/her N_p papers have at least h citations each, and the other (N_p − h) papers have no more than h citations each

Hirsch suggested that, for physicists, a value for h of about 10–12 might be a useful guideline for tenure decisions at major 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.