The most commonly used metric related specifically to authors is the h-index. Google Scholar also produces an i10 index if an author creates a profile in that database.
Hirsch developed this metric in 2005, attempting to measure the productivity and citation impact of a particular scholar. In his paper below he states, "A scientist has index h if h of his/her Np papers have at least h citations each, and the other (Np−h) papers have no more than h citations each.” Put simple, this is the intersection of the number of papers published and the times they have been cited. Additionally, in this paper, he suggested thresholds for physicists at various levels, but these thresholds do not hold true for all fields.
h-index is calculated based on database-specific citation count data in each of the following three databases. Because databases have differing amounts of journals indexed and also because their methods of counting citatable articles varies, each may produce a different h-index. Check with your department about which metric would be most appropriate to report in cases of promotion and/or tenure.