In this era, the technology is still rare in fishing industry. That’s the reason why this tool is created. This tool is able to calculate the fingerlings in large numbers with the right priority calculation accuracy and fast. This tool uses arduino mega 2560 as microcontroller, and some of the other major components such as sensors to detect the presence or absence of fish passing and LCD as a medium to display the number of fish that are detected by the sensor. The fingerlings pass twice calculation process that is manual counting process and using the tool. After passing this process, percentage calculation accuracy tool will appear. After designing process, manufacturing, and experiments finish, the results are satisfactory with an average percentage of 98.81 % accuracy of the calculation, in the other words 1.19 % is percentage error.