A part or amount considered in relation to a whole: What is the proportion of helium in the atmosphere? A relationship between things or parts of things with respect to comparative magnitude, quantity, or degree: the proper proportion between oil and vinegar in the dressing. A relationship between quantities such that if one varies then another varies in a manner dependent on the first:"We do not always find visible happiness in proportion to visible virtue"(Samuel Johnson). The agreeable or harmonious relation of parts within a whole: The statue seems out of proportion. often Dimensions; size: First measure the proportions of the room. Mathematics A statement of equality between two ratios. Four quantities, a, b, c, d, are said to be in proportion if a/b = c/d . To adjust so that proper relations between parts are attained: Have you proportioned the oil in the dressing properly? To form the parts of with balance or symmetry: The artist proportioned the figure nicely.