When you select a font in desktop applications, you can specify a style such as bold or slanted, and a point size.

We specify font size without pause, but what does it mean when a digital font is 12 points? It’s a fairly simple concept that dates back to the dawn of printing presses, but one that changed when typesetting joined the digital world.

Type point-size gauge measuring the font size of an uppercase A

Point Size Started with Printing Presses

Point-size specification has its roots in printing press lockups, which are wood-and-metal forms inside which lines of type are assembled into full pages ready to go to press. Each line of type has a height that is measured in points. In physical terms, a point is 1/72 of an inch, which means that 72-point type is an inch tall, and 12-point type is 1/6 of an inch.

Gutenberg-style press form lockup

Metal press lock-up of a Gutenberg-style press chase.
Photo by Kristian Bjornard under Creative Commons license.

The Leap to Digital Type

When the prepress world moved from metal to digital type, processes changed greatly, but the old terminology carried on. In today’s digital world, point size refers to the height of a typeface’s bounding box or em-square, which is somewhat larger than the distance from its lowest descender to its highest ascender.

Text sample showing ascender and descender lines

How Consistent Are Point Sizes?

Within a well-made typeface family, point size is consistent across its various styles, so 14-point slanted type looks right when it appears inline with its unslanted 14-point siblings.

Text sample illustrating how slanted and regular text have the same height

When you examine bounding boxes of the same point size across several typefaces, you’ll note that they are consistent in height as shown below.

Six type samples, all of the same point size, but of varied physical size

If the bounding boxes are consistent, why do fonts with the same point size appear quite different in size when rendered? It’s because the final appearance of an individual font depends on several decisions made by its designer, including:

  • Whether the font’s glyphs are round or oval in shape
  • Whether the widths of its characters are narrow, normal or wide
  • How high the font’s x-height is
  • Where its baseline appears within its bounding box
  • How large the spacing is above its ascenders and below its descenders

The Realities of Digital Point Sizes

All these factors illuminate that without the physical reality of printing forms and blocks of type, point size is really just an approximation of font size. In most cases, the actual size of digital character outlines are smaller than their physical point size.

To complicate matters, some characters such as accented capitals can extend beyond the top of their bounding boxes. In most cases, digital fonts provide enough room to accommodate taller caps, but designers should be aware that they might need to manually adjust a line of type to compensate for this out-of-bounds behavior.

So What’s the Point?

If you boil all this down, here are some simple lessons about point size in digital type:

  • Point sizes are based on real type sizes used by printers of yesteryear.
  • Points indicate the approximate heights of digital type.
  • The actual size of digital type also depends on its style, weight and metrics.
  • Within a single font, greater point sizes are always larger than lower ones.
  • Point size is consistent across styles within a well-designed font family.
  • Different digital fonts with the same point size aren’t necessarily the same actual size.

So there’s the point of this post about point size.