I want to draw readers' attention, particularly that of @AaronShekey, to the fact that the W3C does not actually recommend setting the line height to 1.5-2.
The relevant recommendations seem to be WCAG criteria 1.4.12 (Text Spacing) and 1.4.8 (Visual Presentation).
Criterion 1.4.12 regarding text spacing reads:
In content implemented using markup languages that support the following text style properties, no loss of content or functionality occurs by setting all of the following and by changing no other style property:
- Line height (line spacing) to at least 1.5 times the font size;
- (etc.)
So this isn't a requirement, or a recommendation, for the line height setting - it's a requirement that if the lines are set to be more spaced-out, the site/webpage do not become unusable or dysfunctional, and no content becomes invisible/inaccessible.
The W3C document entitled "Understanding Success Criterion 1.4.12: Text Spacing" reiterates this (emphasis mine):
The intent of this Success Criterion (SC) is to ensure that people can override author specified text spacing to improve their reading experience.
The recommendation is to support overriding of settings to cater to the needs of some readers - not to change the default settings.
WCAG criterion 1.4.8 regarding Visual presentation reads:
For the visual presentation of blocks of text, a mechanism is available to achieve the following: (Level AAA)
... snip ...
Line spacing (leading) is at least space-and-a-half within paragraphs, and paragraph spacing is at least 1.5 times larger than the line spacing.
So, not the default, but achieveability through some mechanism.
@MaxD linked to a "techniques" document which mentions the importance of providing line spacing between 1.5 and 2, but:
- That document is not the official WCAG.
- "Providing" doesn't mean "having that be the default". The actual WCAG clarifies that the intent is providing the mechanism for making that setting. For example, a site-level per-user setting to that effect.