In this study, an electronic measuring instrument was designed to measure temperature and relative humidity. The method used to measure relative humidity is the Psychrometric Hygrometry method. In this method, relative humidity is calculated from measurements of dry-bulb and wet-bulb temperatures. The temperature measured directly with a thermometer is the dry bulb air temperature. The wet bulb temperature is obtained from a thermometer with the tip connected to a water tube via a wick. The wet bulb temperature is affected by airflow. Because the tip of the wet bulb thermometer is connected to the water, the dry bulb temperature is always higher than the wet bulb temperature. The value of these two temperatures is then used to calculate the relative humidity. Therefore, two temperature measuring instruments are required to measure relative humidity. The designed measuring instrument can be used to measure 4 temperature points and 4 relative humidity points. Therefore, the total number of temperature sensors used is 12. In general, the designed measuring instrument is capable of measuring temperature and relative humidity with an error below 5%. The instrument is capable of measuring temperature with an error below 2%. When compared to the calculation of relative humidity with dry-bulb and wet-bulb temperatures measured using a hygrometer, the measuring instrument has an error of 4.29%. When compared to the DHT22 humidity sensor, the error is 4.5%.