This article presents digital drafting techniques to reveal encoded ratios underlying the eleventh- and twelfth-century brick compositions at the Great Mosque of Isfahan. I use this evidence to argue that the skill of conceptual subitizing (the mental manipulation of quantities) enabled craftspeople to translate and alter designs into varying scales and contexts. A reinforcing process of sustained use and appreciation cemented these designs in the visual repertoire of medieval Isfahan, led to a hierarchy of their use, and opened a path to symbolic interpretations. While a lack of textual commentary on the Great Mosque’s many renovations has hitherto proved a barrier to interpretation, digital modes of processing and interpreting offer insights into areas the written word cannot. This conveys knowledge essential to reevaluating how signification and meaning were constructed in the medieval Islamic world.