2013 California Standards for Accessible Design Pocket Guide

11B-703.5.8 Character spacing.

Character spacing shall be measured between the two closest points of adjacent characters, excluding word spaces. Spacing between individual characters shall be 10 percent minimum and 35 percent maximum of character height.  [S.H.  Visual character spacing not addressed by 2010 and earlier versions of CBC, or by 1991 ADAAG.]