Three-quarter view

The three guys in the painting above are all depictions of King Charles I, painted from different viewpoints by Anthonis van Dyck in 1636. In the middle we see a frontal view (“en face”), on the left a side view (“en profile”), and the most intriguing is the one on the right: the three-quarter view (“en trois quarts”). So here is the question that has bugged me for some time. Why is it called three-quarter, or 3/4? Three quarters of what?

I have taken several actions to get an answer. Of course I browsed the web extensively. And trust me, I know how to find things. I have asked the artists in my family who have taken drawing classes at professional academies. I also posted a question on the fabulous website Aardvark. All the answers came down to this: if the three-quarter view is 3/4 then the other two must be 2/4 and 4/4. There was no consensus on whether 2/4 corresponds to the frontal view or the side view. And no one could answer my question; which view is 1/4 or 0/4 in this line of reasoning? Views of the back of the head?

My guess is this. The 3/4 refers to the proportion of the width and length of the head as it is painted on the canvas. In the drawing manuals I consulted, they set the length of the head as the standard equal to 1. The rest of the body is expressed as “number of heads” or “fraction of head length”. For example, the average person is 7 1/2 heads tall. I also found rules for drawing the head in frontal view with proportion 2/3 = 0.67 and from the side with proportion 7/8 = 0.88. Nowhere did I find an explicit mention of 3/4 = 0.75 for the “three-quarter” view.

The three views of King Charles I fit these rules quite well. The frontal view is very close to 2/3 although the side view is somewhat less than 7/8 that the rule prescribes. Most importantly, the proportion of the three-quarter view is indeed very close to 0.75.