Proportional Measurement of Buddha's Head in Thangka Painting
The upper part of the Usnisa, also called the "Jewel-Tip" (nor.tog), is two small units in height. Narrow at the tip and wide at the base like a jewel. Below this, the main part of the Usnisa is four small units high and four wide. It is in the shape of an inverted alms-bowl or a pile of grain.
The hair of the head is four and one-half small units from crown to hairline and shaped like an inverted pan. The forehead is nine small units wide; from the center of the hairline, it curves gradually to both sides like a bow.
At a point four small units below the hairline, in the center of the forehead, is the Urna or mid-brow point (mdzod, spu). Formed by thirty-two fine white hairs coiled to the right. It is drawn as a round dot with a diameter of one small unit.
The eyebrows begin with three basic units (or three-quarters of a small unit) to the right and left of the urna. They are four small units long, one basic unit thick in their centers. And curved in shape like crescent moons.
One small unit below the Urna is the lower lines of the eyes. The eyes are drawn as the "gaze of the fourth level of Dhyana (meditative stability)." And are one small unit to either side of the central vertical line. The eyes are four small units long and one basic unit wide, shaped like bows. The upper lines are tapered thinner, the lower lines thicker, and curved upwards.
The inner and outer corners of the eyes are red for one-half of a small unit's width. The central white of the eyeball being three small units wide. In the center is the Iris (also, ‘kalita'), round and one small unit (diameter).
In the center of that is the Pupil ('sutali'), round with a diameter of one-fifth of a small unit. Surrounding the pupils is a band one-fifth of a small unit wide, called the 'Rim' (mu.khyud).
Surrounding the pupils is a band one-fifth of a small unit wide, called the 'Rim' (mu.khyud).
This band is traditionally yellow for peaceful divinities. And red and blue for the wrathful ones. The pupil is black, the eyeball veined with red. The eyes are clearly detailed, wide, and lovely. With the outer corners pointing towards the orifices of the ears.
From the mid-brow point (Urna) to the tip of the nose is a distance of four small units. And the tip of the nose is two small units wide. The bridge of the nose between the two nostrils is one-half of a small unit wide. The nostrils are each one-half of a small unit wide. The fleshy outer rims are each one-half of a small unit in thickness. Although some artists draw the nostrils and bridge of the nose one small unit each in width, this is somewhat lacking in beauty.
From the base of the nose to the upper lip is a distance of one small unit. The area above the upper lip has the shape of a lotus petal. The upper lip is one-half of a small unit thick, while the middle of the lower lip is a full small unit in thickness. The distance between the dimples is four small units. The lips are curved upwards for one small unit at the corners, in a gentle smile.
There are some traditions where the upper and lower lips are drawn of equal thickness. And the dimples of the smile curving up only six grains (three-quarters of a small unit).
Beneath the lower lip, at a distance of two small units, is the Chin, four small units wide and rounded.
The Earlobes are two small units wide from the outer edge of the face, and four or four and one-half small units at the middle part. The lobes reach to just below the level of the chin.
Besides the jaw, in front of the orifices of the ears, are lobes of flesh shaped like flower petals. They are one-half a small unit wide and high. The orifices themselves are also one-half a small unit long and wide. The folds, termed (komo), are one small unit wide and high. It is encircled by the two-grain wide folds termed the 'shaku’. Outside these are the folds termed 'kani (ka.ni), which are two small units lengthwise and one across. Outside these are the rims of the upper ears, called 'curves' ('khyil.ba), one-half a small unit in width. They arched over the top of the upper ears to curve in to join the head. And circling down to meet the earlobes: these are also termed 'beka patterns'.
Source: Principles of Tibetan Art, by Gega Lama