Free Readability Checker — 7 Formulas, Sentence Map & Famous Benchmarks

The Flesch Reading Ease score runs from 0 (unreadably complex) to 100 (extremely simple). Here's how to interpret it and what to target by content type: 90-100: Very Easy — 5th grade level. Consumer product instructions, children's content. 80-90: Easy — 6th grade. Conversational copy, social media, simple emails. 70-80: Fairly Easy — 7th grade. Most marketing copy, landing pages. 60-70: Standard — 8th-9th grade. Blog posts, news articles, general web content. This is the sweet spot for most audiences. 50-60: Fairly Difficult — 10th-12th grade. Professional B2B content, technical blogs. 30-50: Difficult — College level. Academic blogs, whitepapers, research summaries. 0-30: Very Difficult — Graduate level. Academic papers, legal documents, medical literature. Google doesn't use Flesch scores directly in its algorithm, but clear, readable content performs better because users stay longer, bounce less, and share more — all of which are indirect ranking signals.

Each formula was designed for a slightly different purpose and uses different inputs: Flesch Reading Ease (1948): The oldest and most cited. Uses sentence length + syllables per word. Gives a 0-100 score where higher = easier. Best for: general writing quality assessment. Flesch-Kincaid Grade Level (1975): Converts Flesch into a US school grade level. Developed for the US Navy to assess technical manuals. Best for: quick grade-level equivalence. Gunning Fog Index (1952): Counts 3-syllable words as "complex." Grade-level output. Best for: journalism and business writing. Robert Gunning created it specifically for newspapers. SMOG Index (1969): Simple Measure of Gobbledygook. Counts polysyllabic words in 30 sentences. The most validated formula for health communications — recommended by the CDC and NHS. Best for: health, safety and legal plain-language compliance. Coleman-Liau Index (1975): Uses character counts rather than syllables, so it's less subjective. Best for: computerised text analysis where syllable counting is unreliable. ARI (Automated Readability Index, 1967): Uses characters per word and words per sentence. Developed for real-time monitoring on typewriters. Best for: objective analysis without syllable ambiguity. Dale-Chall (1948, updated 1995): Compares words against a list of 3,000 familiar words. Grades difficult unfamiliar words more harshly. Best for: educational and children's content assessment.

The benchmarks show where well-known published texts score, giving you real-world context for your own score. Here are the reference points used: Harry Potter (J.K. Rowling): Flesch ~72 — This is the target for young adult and accessible general fiction. Rowling's prose is famously readable. New York Times: Flesch ~65 — The standard for quality journalism. Clear to educated adults but not dumbed down. Harvard Business Review: Flesch ~43 — Academic business writing. Appropriate for professional audiences. Academic Research Papers: Flesch ~30 — Dense, specialised language assumed for expert readers. Insurance Policies: Flesch ~16 — Notoriously difficult. Often cited as a readability failure case study. Use the benchmark scale to quickly understand your text's difficulty in concrete terms. "I'm similar to an NYT article" is more intuitive than "I scored 63 on Flesch."

Vocabulary richness is measured by the Type-Token Ratio (TTR): the percentage of unique words out of total words. A TTR of 60% means 60 in every 100 words are distinct. Why it matters: High TTR suggests varied, precise vocabulary — a mark of skilled writing. Low TTR indicates repetitive, formulaic language that can feel monotonous to read. Important caveat: TTR naturally decreases in longer texts because common words (the, and, is, you) inevitably repeat. For short texts (under 200 words), TTR above 70% is excellent. For medium texts (500-1000 words), 50-65% is strong. For long texts (2000+ words), 40-55% is expected and acceptable. When improving vocabulary richness: identify the most repeated non-stop words from our overused words analysis, and replace some instances with synonyms where meaning is preserved. But don't sacrifice clarity for variety — precision is more important than diversity in technical writing.

The sentence difficulty map displays one horizontal bar per sentence in your text. Each bar's length represents the number of words in that sentence. The colour indicates difficulty: 🟢 Green (≤15 words): Short, easy sentences. Readers process these instantly. 🟡 Yellow (16-25 words): Moderate length. Acceptable but watch the density. 🟠 Orange (26-35 words): Long sentences. Each one is a reading challenge. 🔴 Red (>35 words): Very long. These almost always need to be split. How to use it: Look for clusters of orange and red bars — those are the sections of your text with the highest cognitive load. Click the Annotate tab to see those sentences highlighted directly in the text, then split the longest ones first. Splitting one 40-word sentence into two 20-word sentences can meaningfully improve your Flesch score. Best practice: no more than 15-20% of your sentences should be over 25 words for general-audience writing.