Proportional symmetry is the concept that elements are both symmetrical and well-proportioned, meaning they are harmonious and balanced in their relationship to each other and the whole. It describes how the parts of an object relate to one another and the overall form in a balanced, pleasing way, a principle found in art, architecture, and even human attractiveness.

Proportional symmetry in architecture refers to the Classical Orders of columns—Tuscan, Doric, Ionic, Corinthian, and Composite—which are defined by their unique and harmonious proportions of shaft, capital, and entablature, creating a visually pleasing and stable structure. Each order, from the simple Tuscan to the ornate Composite, establishes a system of ratios, often based on the column's diameter, to ensure proportional balance and rhythm within a building.