Ring Size Converter by Jesus Peregrina de la Puente is a free Android application designed to help users determine the size of a physical ring in different standards from around the world and find its equivalent size in other countries. The app provides internal perimeter length, internal diameter, and actual size in the selected standard, as well as in both the selected and source standards.

Users can choose to display measurements in either metric or inches by checking or unchecking the "in metric" checkbox. The ruler changes its markers based on the selected standard. Additionally, the app offers extra sizes for some standards that are only visible when the user selects the "extra sizes" checkbox.

Overall, Ring Size Converter is a convenient tool for anyone who needs to determine ring size across different standards and countries.