Accurate measurement of the WSR-88D Antenna Gain is important in computing accurate Reflectivity of weather data. Proper calibration of the Open Radar Data Acquisition (ORDA) receiver path and noise test path is critical in obtaining accurate estimates of the WSR-88D antenna gain. This paper presents a discussion of the antenna gain calibration path, explains the algorithms used to compute antenna gain and beamwidth, presents the manufacturer's antenna gain and beamwidth measurements and provides actual field data from WSR-88D ORDA sites.