Readability measures how difficult a text is to read and understand. Modern readability formulas combine two main signals: sentence length (longer sentences are harder to hold in working memory) and word complexity (words with more syllables or characters are harder). The best-known formulas are Flesch Reading Ease, Flesch–Kincaid Grade Level, Gunning Fog, and SMOG.
Consider two sentences with the same meaning. "We utilised sophisticated methodologies to facilitate comprehension" scores as difficult — long words, abstract nouns. "We used simple methods to help people understand" scores as easy — short words, plain verbs. Formulas capture exactly this kind of difference, which is why editors, teachers, and content teams use them to keep drafts at an appropriate level. A common target for general web writing is a US grade level of about 7–8.
Where is it used? Newsrooms aim for broad accessibility, government and legal "plain language" initiatives mandate readability thresholds, healthcare materials are often required to sit at grade 6 or below, and SEO writers use scores to keep pages skimmable. The important nuance: readability scores are heuristics, not measurements of comprehension. They see only sentence and word length, so they cannot detect jargon used in short words, ambiguous pronouns, poor logical flow, or bad layout. A text can score "easy" and still be confusing. Use scores as a directional signal — shorten sentences, cut needless syllables, prefer active voice — not as a grade of quality. Paste a draft into our Word Counter to see length statistics that drive these formulas.