The standard is changing. Before the last decade or so, the ideal ratio included the lips split into thirds with ⅔ being the bottom lip and ⅓ being the upper lip. However, now to the increased popularity of plump, defined lips, the standard is slanted towards more of a half and half ratio.
Ultimately, patients can decide what look they like best. Our injectors simply ensure the lips remain naturally proportionate based on the ideal ratios. Also, the ideal ratio may depend on the starting anatomy of the lips and what is possible.