Canon: From scripture to point size

To most people, a canon is a principle, rule, or body of standards: the literary canon, the canon of physics, the canon law of the Church. The word comes from the Greek kanon, meaning a measuring rod or standard. In each of these cases it names something authoritative that sets bounds.

In industrial printing, canon is something much more concrete. It is a specific size of metal or photographic type, standardized at 48 points. One point equals 1/72 of an inch, so a canon letter stands 48/72 of an inch tall, or two-thirds of an inch from top to bottom. This measurement was historically chosen because it was the size required to print the canons of the Church, the authoritative rulings and texts of ecclesiastical law. The physical standard for setting these holy canons became the name of the type size itself.

The connection between the two meanings is direct: the Church's canons gave the type size its name and scale. But by the time industrial printing had standardized type sizes into a named hierarchy, canon had become a technical term detached from its scriptural origin. A printer asking for canon type was not thinking about church law; they were calling for a particular piece of metal or film bearing letters of exactly 48 points.

Canon sits in a family of named type sizes that grew from practical necessity and Christian history. The largest size in common use was called two-line pica; canon was smaller than some medieval ecclesiastical fonts but larger than great primer (36 point). These names accumulated over centuries of printing, each one tied to a use or origin now mostly forgotten.

Today the term is largely obsolete in digital typography, where any size can be specified numerically. But in metal type foundries and in the study of printing history, canon remains the exact name for a 48-point letter, a direct inheritance from the measuring rod that once standardized the word of God.