The aspect ratio or proportions of a two-imensional shape is the ratio of its longer dimension to its shorter dimension. It is also applied to two characteristic dimensions of a three-dimensional shape, especially for the longest and shortest 'axes' or for symmetrical objects (e.g. rods) that are described by just two measures (e.g. length and diameter). In such cases, the aspect ratio may evaluate to a value less than one (e.g. consider very short and very long rods). The aspect ratio of a torus is the ratio of the major axis R to the minor axis r.