Check readability across 5 industry-standard formulas simultaneously: Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog, SMOG Index, and Coleman-Liau. Highlights long sentences, shows reading time, and gives target audience benchmarks for web, blog, and academic content.
Paste any text — blog posts, landing page copy, email campaigns, product descriptions, academic writing. The tool works with plain text and strips HTML automatically. Real-time updates show word count, sentence count, and syllable count as you type.
Five readability formulas run simultaneously: Flesch Reading Ease (0–100 scale), Flesch-Kincaid Grade Level (US school grade), Gunning Fog Index (years of education required), SMOG Index (education level), and Coleman-Liau Index (character-based formula). Each score is shown with a gauge and audience interpretation.
Long sentences (over 25 words) are listed individually with character counts — these are primary candidates for splitting. The tool shows the percentage of complex words (3+ syllables), reading time estimate, and target score benchmarks for different content types (web content, email, academic, legal).
The Flesch Reading Ease score (Rudolf Flesch, 1948) measures how easy a text is to understand on a scale of 0–100. Higher = easier. The formula is: 206.835 − (1.015 × average sentence length) − (84.6 × average syllables per word). Score ranges: 90–100 = Very Easy (5th grade), 70–80 = Fairly Easy (6th grade, standard web content), 60–70 = Standard (7th–8th grade, ideal for most web copy), 50–60 = Fairly Difficult (10th–12th grade), 30–50 = Difficult (college level), 0–30 = Very Difficult (professional/academic). Target 60–70 for general web content.
The Flesch-Kincaid Grade Level formula converts the same basic measurement (sentence length and syllables per word) into a US school grade equivalent. The formula is: (0.39 × average sentence length) + (11.8 × average syllables per word) − 15.59. A score of 8 means the text is appropriate for an 8th grader. For most web content, a grade level of 7–9 is ideal. Legal documents and academic papers often score 12+. Technical documentation typically targets grade 10–12. The grade level and Flesch Reading Ease are inversely related.
The Gunning Fog Index (Robert Gunning, 1952) estimates the years of formal education required to understand a text on first reading. The formula counts "complex words" — words of three or more syllables, excluding proper nouns, compound words, and common two-syllable verbs. Formula: 0.4 × (average sentence length + percentage of complex words). A score of 12 corresponds to US high school level. The Wall Street Journal targets a Fog score around 11. Most web content should aim for 8–12.
The SMOG (Simple Measure of Gobbledygook) Index, developed by G. Harry McLaughlin in 1969, predicts the grade level needed to fully understand text. It focuses specifically on polysyllabic words (3+ syllables) and uses the formula: 3 + √(polysyllabic word count × (30/sentence count)). SMOG is considered more accurate than Flesch-Kincaid for healthcare materials and consumer information because it counts all polysyllabic words rather than averaging syllables per word. US health agencies typically target SMOG scores of 6 or below for patient-facing materials.
Readability affects SEO indirectly through user engagement signals. Content that is difficult to read has higher bounce rates and shorter dwell time — users abandon the page quickly when they struggle to understand it. Google's algorithms measure these engagement signals (particularly on mobile, where dense text is especially hard to read). Additionally, readable content generates more shares, more backlinks, and more return visits. Yoast SEO, one of the most widely used SEO plugins, includes a readability analysis specifically because Google's quality guidelines emphasise content being written for humans first.
Web copy / blog posts: Flesch 60–70, Grade Level 7–9. Email campaigns: Flesch 65–75, Grade Level 6–8 (lower reading level = higher open and click rates). Product descriptions: Flesch 70–80, Grade Level 6–8. News articles: Flesch 55–65 (Associated Press style). Legal documents: Grade Level 12+ is typical but improving to 10 is beneficial. Healthcare / patient materials: Flesch 70–80, SMOG 6–8. Academic journals: Flesch 20–40 is standard but not desirable for web. Children's content: Flesch 80–90.
