According to the Roman architect Vitruvius, in a well-proportioned body the height of the head (from chin to crown) should occupy 1/8 or 0.125 of the total body height. Leonardo’s Vitruvian man depicts the ideal ratio of 0.125 between head and body (head-body ratio or HBR). As Albrecht Durer later recognized, real human bodies often deviate from this ideal. Much of the deviation is due to stature. Several years ago I analysed anthropometric datasets from almost 5000 NATO personnel in four countries, and found that there is a consistent relation between stature and HBR: People over 192cm (6’ 3”) tall tend to have a HBR of 0.11 or less, while people below 165cm(5’ 1”) tend to have a HBR of 0.14 or more.
Classical sculptors may have used HBR to convey the stature of the human figure. Statues of David such as Michelangelo’s famous David in the Accademia, Florence, have a HBR over 0.14 (consistent with his small stature), whereas statues of tall figures such as the Roman bronze Hercules have a HBR of 0.11 or less.
The drawing shows these two statues on either side of an Ancient Greek Riace Warrior, which has the ideal HBR of 0.125. The figures are drawn at relative heights that are appropriate for their HBR, though they bear no relation to the physical size of the sculptures. The statue of David stands 4.09m tall, the Riace Warrior stands at 2.0m, and the Capitoline Hercules is 2.41m tall.
Giacometti’s “Standing Woman I” (J. Paul Getty Museum) has a very all HBR of 0.09. In “Three Men Walking II” (Metropolitan Museum of Art) the three figures have tall HBRs below 0.10.
Perceptual research which I reported in 2010 showed that it is possible to manipulate a viewer’s impression of the stature of a figure in a photograph by manipulating the figure’s HBR.
So perhaps Giacometti’s sculptures and portraits have small heads to induce a paradoxical impression of monumental size and stature even in a physically small object. Some of Giacometti's whole figure sculptures have disproportionately large feet as well as a small head. This may heighten the paradoxical impression that one is viewing a very tall figure in which the legs are much closer to the eye that the upper body.
Mather, G. (2010). Head – body ratio as a visual cue for stature in people and sculptural art. Perception, 39(10), 1390-1395.