*Where did these numbers come from? -- Per capita expenditures were collected from Wisconsin's 2010 Public Library Statistics, compiled by the State Division for Libraries, Technology and Community Learning (DLTCL). The return on investment is calculated by dividing each library's annual per capita expenditure by 12 (the number of months) to get a monthly per capita expenditure. The formula then divides the total value received each month by the monthly per capita expenditure.

This calculator is an adaptation of projects by the Maine State Library and Library Research Service, a unit of the Colorado State Library and the Colorado Department of Education that is operated in partnership with the Library and Information Science (LIS) Program, Morgridge College of Education, University of Denver.