I'm designing screens for both Mobile & Digital signage, the screen may vary from a smartphone to a 80" screen. I wanted to know how to determine the appropriate font size for fields like Title, Subtitle, Category, Description, and Price.
I would suggest to try the fluid typography approach. This concept helps you to build the universal typography rules for all the screen sizes.
Other than that, keep in mind that the contrast of the font sizes is very important for the readability. There's a great article on the web typography to use as a checklist.