Do you know how to tell the different size of paper cups?

Paper Cup Sizing may sunds difficult to distinguish. Whenever someone asks what size of the coffee cup do I need? I suddenly felt so confused. Here is a picture below to see the difference. Especially when we answer customers' question, we need clearly know the top diameter and bottom diameter,and even the height. 

For chinese people, we usually use Millimeters （ml） instead of ounces (oz).  Some customers may say they want  240ml to 300 ml cups, we have to quickly swap Millimeters for ounces.  I think this picture below is helpful to tell you about the different sizes of paper cups