Which font size and font spacing?

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Don’t use a poorly readable font size for the sake of design. In user assistance, readability is more important than beauty.

Keep in mind:

Many people have poor eyesight. If you can read something well, this doesn’t mean that others can also read it well.

Your document may be read in places or under conditions where reading is more difficult than in your office.

Audiences that aren’t used to reading long texts may be discouraged by small fonts.

Type smaller than 10 points usually slows down all readers.

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General recommendations

Adequate font sizes for printed manuals usually are:

on small paper sizes: body text from 8.5 points up to 10 points, headings up to 20 points

on large paper sizes such as A4 or Letter: body text from 10 points up to 12 points, headings up to 24 points

if the manual is likely to be read under difficult conditions: body text up to 14 points

Adequate font sizes for online help usually are:

10 points or 11 points for body text

14 points for headings

Other factors that influence font size:

In texts that are mainly used for looking up small pieces of information, eye exhaustion can be neglected. So you can use a smaller font size here. Dictionaries are a typical example of this.

Also base your decision on the specific font that you’re using. Not all fonts of a given font size actually have the same character size. For example, in one font with a font size of 10 points, letters may be 2.5 mm high, whereas in another font with a font size of 10 points, letters may only be 2.0 mm high.

Font size in headings

The font size is the most important way to visualize the hierarchy of headings (other ways are the font weight, color, and space before and after the heading; see Heading paragraph styles).

The size runs from biggest to smallest, and the typeface runs from boldest to lightest.

In a printed manual, use at least a difference of 3 points between the levels of headings (for example, 20, 17, 14 points). Otherwise, readers might be unsure of what level they’re looking at.

In online help, topics are more independent. Here, use the same font size for all topic titles, regardless of where they’re located within the hierarchy of the table of contents.

Optimizing font spacing for large font sizes

For font sizes up to 16 points, the default font spacing usually provides the best results.

If you use font sizes that are larger than 16 points (mainly in headings), you often need to decrease the default font spacing for better readability. As a positive side effect, this also makes the headings shorter and reduces the risk of having unwanted line breaks.

If you use a light font color on a dark background (inverted text), increasing font spacing usually also improves readability.

In online help, slightly increased font spacing can improve readability as well, especially if you don’t use a font that’s optimized for reading on screen.


Which font?

What page size?

What page margins?

What line length?