The loT based automatic evaporation measuring instrument was designed in this research to replace the conventional measuring instrument, hook gauge and stilling well. This measuring instrument was composed of two components, namely NodeMCU microcontroller and infrared distance sensor. The measurement data is stored and displayed on the ThingSpeak website. To know the performance of the measuring instrument, conducted several tests. They are resolution tests, accuracy tests, short and long term stability test, and wireless communication between the instrument and server test. Based on the test result, obtained the resolution of the instrument was 2 mm, the accuracy has obtained the error of 2.34 mm by using the regression method and 0.34 mm by using a look-up table and interpolation method. The short stability reached above 95%. The standard deviation of the long term stability test was 0.157 mm, measured as much 100 times for 100 hours. Therefore, the measuring instrument successfully connects to the server and is able to send data properly.