Calculating with roll diameters is a bit tricky. With this app you can calculate beforehand how big the diameter will be. The app has several options.
With this calculator you can easily compare or calculate the diameter, length or thickness of a roll. It doesn't matter whether paper roll, foil, crepe, aluminum, laminate, carpet...
I have been working in a paper processing factory for a long time (see info) and have a lot to do with paper rolls, aluminum rolls and polyethylene (PE) coatings. Very often you want to know something quickly about a role. That's why I wrote the app. The app was written with App Inventor, which means that I am not a professional app programmer and have only limited settings.
If you find errors or miss another useful calculation with roles, please write to me. Maybe I can do something.