Information on the Association of Research Libraries (ARL) data survey is presented, along with a quantitative index for the university libraries of the Association of American Universities (AAU). Ten quantitative measures of holdings, expenditures, and staff size for the AAU libraries from the 1981-1982 annual ARL survey are converted to an index of summary size, distributing these AAU libraries along a normal curve. The index permits quantitative comparisons of academic libraries, singly and as a group, with other academic libraries. Through factor analysis, 10 variables emerge as characteristic of AAU library size: volumes held, volumes added (gross), microform units held, current serials received, expenditures for library materials, expenditures for binding, total salary and wage expenditures, other operating expenditures, number of professional staff, and number of nonprofessional staff. Component score coefficients or weights for the 1981-1982 AAU academic library data are shown, along with the calculation of a library's 1981-1982 index score. The index scores for 52 academic libraries are provided. Information is included on the specific quantitative measures for the libraries. (SW)