What is Readability?
Readability is the ease with which text can be read and understood, determined by factors including vocabulary complexity, sentence length, typography, line length, spacing, and contrast.
How it works
Readability operates at two levels: linguistic readability (how complex the language is) and visual readability (how the text is presented). Linguistic readability is measured by formulas like Flesch-Kincaid (which considers syllable count and sentence length) and is improved by using shorter sentences, simpler words, and active voice. Visual readability depends on font size (minimum 16px for body text on screens), line height (1.4-1.6x font size), line length (45-75 characters optimal), contrast ratio (minimum 4.5:1 per WCAG), and font choice. Both dimensions interact: even simple text becomes hard to read with poor typography.
Applied example
A government benefits website written at a 12th-grade reading level is rewritten at a 6th-grade level following plain language guidelines. Combined with increasing font size to 18px and line height to 1.6, the changes reduce user errors on application forms by 30% and support calls by 25%.
Why it matters
Readability is the gatekeeper of content effectiveness: no matter how valuable the information, it fails if users cannot or will not read it, making readability optimization one of the highest-return content investments.
