This brief describes a new method for states to determine how well their charter school facility needs are being met with state policies, both at present and in the future as the number of charter schools increases. The brief also illustrates how this new approach, called a Charter Facility Index, can be used in practice, with three state examples. Finally, the brief covers next steps in refining and implementing the new method. The benefit of the Charter Facility Index is that it quantifies "how much" of facility needs the state is meeting, both now and projected into the future. The Charter Facility Index also considers likely growth in charter school enrollment and the number of charter schools in a state. In addition, the Charter Facility Index allows policymakers to determine the likely impacts of any proposed changes in state policies. By using this method, policymakers can determine how to use a suite of policies to meet the facility needs of charter schools in their states. [For the summary, "Building for Success: How States Can Address Charter School Facility Needs. Policy Summary," see ED609271.]