The 2/3 rule is a popular interior design guideline used to ensure proper spatial proportion between a living room sofa and the primary accent surface, such as a coffee table. The rule states that the length of your coffee table should ideally be about two-thirds (66%) the total length of your sofa. This proportion prevents the table from either looking dwarfed by a massive sectional or overwhelming a smaller standard couch, preserving visual balance in the room.