Is there an ideal proportion for mouth size compared to the face?

Thank you for your photograph and question.  The decision to pursue any beauty enhancement procedure is a personal one and your decision to have a lip augmentation depends on your desired goals.  You would be an excellent candidate for increasing the overall volume of your lips, while maintaining its overall shape, but only pursue treatment if YOU want it.  Hope this helps. 

Hi 13almw,Your horizontal lip width is within normal proportion for your face according to the ideal facial proportion aesthetics, however, beauty evolves and trends change with time and location, like for instance, in Asia, thinner lips are still considered more feminine, while in Western Culture, fuller lips is considered more attractive. The fullness of the lips is more on a personal preference, but your natural lips (as on the photos) are good and in proportion with your facial features.