The calibration of a wind tunnel is a necessary, yet often neglected, process needed to ensure accurate and repeatable test data. In general, a wind tunnel calibration program encompasses many related topics—basic operating condition calibration, flow quality mapping, wall interference, and model blockage corrections are all topics that can be addressed as part of a tunnel calibration program. However, it is not practical to address all of these topics in a single document, so the scope of this recommended practice has been defined as the empty test section calibration of subsonic and transonic wind tunnels. This American Institute of Aeronautics and Astronautics (AIAA) Recommended Practice is intended to (1) provide an overview on the calibration of subsonic and transonic wind tunnels and (2) provide a basis for commonality within the wind tunnel community in the area of wind tunnel calibration. This document is a compilation of input from several wind tunnel operators and users that summarizes the best practices and recommendations from these experts.