Twelve points make one pica. The pica is the larger unit of the traditional typographic system, used for measuring column widths and page areas where the point measures type size — and the twelve is the same duodecimal logic as inches to feet.
About the units
A pica is 12 points, which under the modern PostScript definition makes it exactly 1/6 inch or 4.2333 mm. It was the working unit of hot-metal and phototypesetting: column widths, gutter measures and page depths were all specified in picas, with points reserved for type size and leading. Newspaper layout in particular ran entirely on picas, and the vocabulary survives in the trade. The historical American pica was 0.166044 inch rather than exactly 1/6, which is where the 72.27 points per inch of the older system comes from.
The exact factor
The factor is exactly 12. Picas are conventionally written with the points after a p — 14p6 means 14 picas and 6 points, which is 174 points. That notation appears in older specifications and in some layout software, and misreading it as 14.6 picas gives 175.2 points, a small but real error. In metric terms a pica is 4.233 mm, so a 20-pica column is 84.7 mm wide.
Where you meet this conversion
Newspaper and magazine layout, where legacy specifications and house styles are written in picas. InDesign and QuarkXPress both support the unit and the p notation. Anyone working with archive layouts, reprints or established editorial templates meets it. Web design has no equivalent, which is why converting a print grid to a responsive layout usually means abandoning the pica entirely rather than translating it.