1. A part considered in relation to the whole.
  2.  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.
  3.  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).
  4.  Agreeable or harmonious relation of parts within a whole; balance or symmetry.
  5.  Dimensions; size. Often used in the plural.
  6. 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 .


Proportions of the face


 "The whole foot goes from the elbow to the wrist, and from the elbow to the inside attachment of the arm to the breast, when the arm is bent. The foot is as big as the whole head of a man, that is, from the bottom of the chin to the greatest height of the head in the way it is drawn here. The foot goes three times into the distance from the tip of the long finger up to the shoulder, that is, to this joint. 

The nose will make two squares, that is, the width of the nose at the nostrils will go twice into the length from the tip of the nose to the origin of the eyebrows. And similarly in profile it is as much from the extreme part of the nostril where it joins the cheek,   to the tip of the nose, as is the width of the surface of the nose from one nostril to the other.

If you divide the whole length of the nose, that is, from its tip to its attachment to the eyebrows, into four equal parts, you will find that the first of the parts goes from the top of the nostril to the bottom of the tip of the nose, and the uppermost part will go from the tear duct of the eye to the attachment of the eyebrows, and the two middle parts will be as large as the eye is from the tear duct to the outer end of the eye. "


"From the roots of the hair to the top of the chest, a b, is the sixth part of the height of a man. And this measurement is equal to..

From the outermost parts of the one shoulder to the other is as much as from the top of the chest to the umbilicus. And this part goes four times from the bottom of the foot to the origin of the lower end of the nose. 

The arm where it separates from the shoulder in front, goes six times into the distance between one and the other outside edges of the shoulders, and three times into the head of a man, and four times into the length of the food, and three into the hand, inside and outside. "