pica

Pica in typography denotes a unit of measurement: one pica equals 12 points, and six picas equal approximately one inch (precisely 0.9964 inches in the PostScript pica adopted by modern software). The word arrived in printing from Medieval Latin pica, which meant a directory or table of ecclesiastical rules — specifically, a table organizing the liturgical calendar printed in black and red ink. That document may have been named for the magpie (Latin pica, from the bird's black-and-white coloring), because the printed table's alternating red and black ink resembled the magpie's plumage.

The typographic unit of measurement called pica was originally a name for a specific type size — roughly 12 points — before being generalized to the measurement itself. Printers in the hand-press era named type sizes after things: pearl, nonpareil, minion, brevier, bourgeois, pica, english, great primer. These names carried no numerical relationship to each other; they were tradition, not system. A pica in one printing house might differ from a pica in another until standardization efforts in the 18th and 19th centuries created the point system that made pica exactly twelve points.

The pica rule — a ruler marked in picas and points — was the essential measuring tool of the compositor, the paste-up artist, and the book designer through most of the 20th century. It measured column widths, line lengths, margins, and image depths. Every dimension of a printed page was expressed in picas and points. When desktop publishing arrived in the 1980s, software like PageMaker and later InDesign preserved the pica as a default unit, carrying it from physical metal type into the digital era.

Today graphic designers work in picas for print layouts and pixels for screen, toggling between measurement systems depending on medium. The pica is specific to printing — you would not measure furniture or architecture in picas — which gives it the quality of a professional argot: a unit that identifies you as someone who works with type. Knowing that six picas make an inch, that a 12-pica column is a standard narrow width, that body text is typically set on a 13-point or 14-point leading — these are the numeracies of the trade.