The main concern related to font size is that text can easily be made too small for many users to read.
Points vs. Pixels
Font size specifications may come in points or pixels where:
- 1 pixel (px) is usually assumed to be 1/96th of an inch
- 1 point (pt) is assumed to be 1/72nd of an inch.
- Therefore 16px = 12pt.
- A commonly recommended minimum for Web pages is 16 px/12 pt.
- The default body size for most browsers is 16px.
- For the color contrast guidelines large text = 14pt bold or 18pt or larger. These are equivalent to 18.67px bold/24 px or larger.
Nine Point Minimum for Footers
If a document contains a footer or footnotes, the minimum size should be about 9 points (or 12px).
Use relative sizes in CSS
Although CSS supports using px or pt units, for font sizing and other items, it is better to use relative sizes in CSS such as ems, or %.
For relative sizes 100% = 1em = 16px/12pt unless another default size is set in the CSS.
Note: An alternate unit rem is similar to em. 1 rem is about 1 em.
If a PowerPoint file is meant to be projected before a live audience (e.g. during a class lecture), the minumum font size should be about 24 points. At smaller sizes, the text becomes illegible on a screen.
Headings and subheadingss can be much larger, between 40-60 points depending on the slide layout.
Last update: August 4, 2020