Diameters, lengths & material thickness calculator for rolls. Comparison between two rolls. The Roll Calculator (the app) is suitable for all kinds of materials that are wound onto a roll, e.g. foil, paper, aluminum, laminates, rubber, lawn, PE coatings, etc. The app has 6 functions: Comparison calculation: Use the data from a known roll to calculate the new roll length. Button1: Calculate the new diameter if you already know the length and diameter of a roll. Button2: Calculate the new rol