Typography Calculator

Print specifications, book layout, and older type foundry documentation all quote sizes in points and picas, while press operators and paper suppliers work in millimetres. Anyone moving a design between a print spec and a screen layout ends up doing these conversions repeatedly.

Note that the desktop publishing point used here is exactly 1/72 inch — the PostScript definition every modern application uses — not the slightly different historical American point.

A typographic point is defined as 1/72 of an inch, which makes one point 0.3528 millimetres. So 12pt type is 4.23mm, 10pt is 3.53mm and 72pt is exactly one inch, or 25.4mm. A pica is 12 points, 4.233mm, and the Continental cicero, based on the older Didot point, is slightly larger at about 4.51mm.

There is a catch that surprises people measuring printed text with a ruler. The point size describes the height of the type's body, the invisible box each letter sits in, not the letters themselves. A capital letter in 12pt text is usually around two thirds of 4.23mm, roughly 3mm, and lowercase letters are smaller still. Two fonts at the same point size can look noticeably different in size for exactly that reason.

Screens use a different base. CSS defines 96 pixels per inch, so one point is 1.333 pixels, 12pt equals 16px and 9pt equals 12px. That is why 12pt in a word processor and 16px on a web page look like the same size.

For web type, convert onward to rem. With the browser default root size of 16px, 12pt becomes 16px and then 1rem. This calculator shows points, picas, ciceros, agates, inches, millimetres, centimetres, pixels and rem together from any one value, with the base font size adjustable for the relative units.