The harmonious relationship of parts to each other or to the whole.

Conceptions of—and attitudes toward—proportion are complicated. What makes something well proportioned? Why are the ratios between some objects considered more pleasing than others? For many, ideas of proportion are complicated by tradition, or by familiarity, but there are a few designated rules that can be useful in thinking through the influence of proportion in design.

The proportion of a space or an object can be described as the relative length of three variables width, length, and height. Proportion in spaces often has a determining role in the function, or use, of that space. A long, narrow corridor cannot be used as a gathering space, but might be ideal for a gallery or a kitchen. A tall, wide space might be too noisy for intimate gatherings, but is ideal for small musical performances. The designer is often presented with a room whose proportions create an opportunity for invention and interpretation, ripe for reimagining based on other principles such as scale and use.

In some interior projects, ideas of proportion and alignment are intimately linked. Even if a room is awkwardly shaped, clever deployment of sectional devices (such as niches, reveals, and recessed elements) can rectify the perceived measurements of the room. Reflective surfaces and patterns can reframe perceptions of space in existing spaces. In any case, the designer should carefully consider the implications of placement, in space or along a wall, of objects in creating an environment crafted to need.