Horizontal motion
Anything from 45 to 75 characters is widely regarded as a satisfactory length of line for a single-column page […] The 66-character line […] is widely regarded as ideal (25).
Sabon at 16px has an alphabet length of 203 pixels, or approximately 152 points. To figure out the horizontal measure, I started with Bringhurst’s copyfitting table (29), which suggests a line length of 26-28 picas (around 450 pixels) for an optimal 66-character line. I was aiming for multiples of 32px across, so I tried 448px. This looked narrow to my eye, and sure enough it yields (in my prose) an average line length of around 61 characters. I tried 512px next — a nice number for us binary-thinking folk — and that hit the nail on the head at about a 68 character line.