Print Font Size pt mm

Standard print font sizes (pt & mm)

Typography runs on the point (pt). The version that matters today is the PostScript / DTP point, which every desktop publishing app has used since the 1980s: 1 pt = 1/72 inch = 0.3528 mm. That pins body text in commercial print to a fairly tight physical band. A 10 pt glyph runs about 3.5 mm in cap height, with a little more once you count the line box.

The usual ranges shift with the medium. Books set their body around 9–11 pt, and most novels land on 10 or 10.5. Newspapers drop to 8–10 pt so they can pack in more columns. Magazines sit somewhere around 9–12 pt, depending on the art direction. And large-print books for children or older readers climb to 12–14 pt, sometimes 16 pt in accessibility editions that follow ISO 9000-style legibility guidelines.

Applications

Pick the body size and you've effectively set the rest in motion, since line length, leading, paper format and signature count all follow from it. Designers also keep two things apart: the nominal pt the menu reports and the optical size the eye actually reads. Optical-size families like Source Serif and Minion ship separate masters for caption (6–8 pt), text (9–13 pt), subhead (14–24 pt) and display (24+ pt), so every glyph is cut for the size it'll print at. The pt ↔ mm conversion earns its keep when you're imposing pages, working to international paper sizes (ISO 216 A4/A5/B5), or specing type for signage.

FAQ

What’s the difference between PostScript point and traditional point? France used the old Didot point, which came to 0.376 mm. The Anglo-American Pica point measured 0.3515 mm. When Adobe built PostScript it rounded the Pica off to exactly 1/72″, and that's where today's 0.3528 mm comes from.

How does pt compare to px on screen? CSS assumes 96 dpi, where 1 pt = 1.333 px. That puts 10 pt at roughly 13.3 px, right in the neighborhood of the 14–16 px most sites use for body text.

Why not just use mm in InDesign? Nothing stops you. The catch is that points divide cleanly into leading and baseline grids (12 pt = 1 pica = a standard text grid), which millimeters don't. Most people keep mm for trim size, margins and bleed instead.