What is readability and why does it matter?
Readability is a measure of how easy a piece of text is to read and understand. It depends on factors like sentence length, word length, syllable count, and vocabulary complexity. Readable writing is not simple writing — it is writing that is efficiently matched to its intended audience. A legal brief for judges can be complex; a product landing page for general consumers should not be.
Research consistently shows that even highly educated readers prefer simpler language. The Plain Language movement in government and healthcare has demonstrated that readability improvements increase compliance, comprehension, and user satisfaction across every audience level.
Flesch Reading Ease
The Flesch Reading Ease score ranges from 0 to 100, where higher is easier. It is calculated from average sentence length and average number of syllables per word. A score of 90–100 is Very Easy (5th grade level, simple everyday English). 60–70 is Standard (8th–9th grade, suitable for most general audiences). 30–50 is Difficult (college level, appropriate for academic writing). Below 30 is Very Difficult, typical of legal documents and scientific papers. Most web content should aim for 60–70.
Flesch-Kincaid Grade Level
The Flesch-Kincaid Grade Level converts the same underlying metrics to a US school grade level. A score of 8.0 means the text is appropriate for an 8th grader. Most popular newspapers and web content target grade 6–8. Academic papers typically score grade 12–16. The formula weights sentence length and syllable count slightly differently than the Reading Ease score, so they do not invert perfectly.
Gunning Fog Index
The Gunning Fog Index focuses specifically on complex words — words with three or more syllables. The formula is: 0.4 × (words/sentences + 100 × complex_words/words). A score of 12 indicates high school level. Fog scores above 17 are considered essentially unreadable for general audiences. The "fog" metaphor refers to the obscuring effect of complex words and long sentences on meaning.
SMOG Grade
SMOG (Simple Measure of Gobbledygook) was developed specifically for health communications and is considered the most accurate predictor of reading comprehension. It counts polysyllabic words (three or more syllables) in a 30-sentence sample and uses a square root formula. SMOG grades tend to run about 1–2 grades higher than Flesch-Kincaid for the same text, which is why health literacy professionals prefer it — it is more conservative.
How to improve your readability score
The two most impactful changes are: shorten your sentences, and replace multisyllabic words with shorter alternatives. "Utilise" → "use". "Subsequent" → "next". "Approximately" → "about". Breaking a 35-word sentence into two sentences of 15–18 words each has a dramatic effect on all four scores. Avoid stacking multiple clauses, qualifications, and parenthetical remarks in a single sentence.