pc

pica

Lengthexact by definition

The pica is exactly 1/6 of an inch, 12 points, about 4.233 mm. It is the horizontal unit of page layout: column widths, margins and gutters are specified in picas while type sizes are specified in points.

Watch out: Its symbol clashes with the parsec, which is also written pc. Nothing in typography and nothing in astronomy is ever ambiguous in practice, but a bare "pc" in a conversion is worth checking.

1 pc 0.0042333333 m