Paste any text and instantly get 3 industry-standard readability scores. Checks Grade Level, Reading Ease, and Gunning Fog Index simultaneously. 100% free, private, no signup.
This tool calculates three industry-standard readability scores simultaneously using pure JavaScript running entirely in your browser. No text is ever sent to a server — your content stays completely private. When you click "Check Readability Score," the tool counts every word, sentence, and syllable in your text, then applies three separate mathematical formulas to produce three distinct readability measurements in under a second.
The syllable counter uses a dictionary-based approximation combined with vowel-group detection, which produces results accurate to within 2–3% of manual counts for standard English text. The sentence detector identifies sentence boundaries using full stops, exclamation marks, and question marks. Average sentence length and average syllables per word are the two key variables that drive all three readability scores.
Each score measures a different dimension of text difficulty. Using all three together gives you a complete picture of how accessible your writing is to different audiences.
| Score | Scale | Target for Most Content | Developed By |
|---|---|---|---|
| Flesch-Kincaid Grade Level | 0 – 18+ | 7 – 9 (blog posts, news) | Kincaid, 1975 |
| Flesch Reading Ease | 0 – 100 | 60 – 70 (general audiences) | Rudolf Flesch, 1948 |
| Gunning Fog Index | 6 – 20+ | 8 – 12 (journalism) | Robert Gunning, 1952 |
The Flesch-Kincaid Grade Level formula is: (0.39 × average sentence length) + (11.8 × average syllables per word) − 15.59. The Flesch Reading Ease formula is: 206.835 − (1.015 × average sentence length) − (84.6 × average syllables per word). The Gunning Fog formula is: 0.4 × (average sentence length + percentage of complex words).
The ideal readability score depends entirely on your audience and content type. Here is a practical guide based on established readability research and content performance data.
| Content Type | Ideal Grade Level | Ideal Reading Ease |
|---|---|---|
| Children's books (ages 6–8) | 1 – 3 | 80 – 100 |
| Young adult fiction | 4 – 6 | 70 – 80 |
| News articles, blog posts | 7 – 9 | 60 – 70 |
| Marketing and landing pages | 5 – 7 | 65 – 75 |
| Business reports | 10 – 12 | 50 – 60 |
| Academic papers | 12 – 16 | 30 – 50 |
| Legal documents | 14 – 18 | 20 – 40 |
Most SEO experts recommend writing blog posts at a Grade Level between 7 and 9. This is not because the audience is unintelligent — it is because shorter sentences and simpler words are faster to read, and reading speed directly affects time-on-page metrics that influence search rankings.
Two variables control all three readability scores: average sentence length and average syllable count per word. Improving either one immediately improves your scores. Here are the most effective techniques used by professional editors and content strategists.
Shorten your sentences. Split any sentence longer than 25 words into two sentences. Each split immediately reduces your average sentence length. The impact is significant — cutting your average sentence length from 22 words to 16 words improves your Flesch Reading Ease score by approximately 9 points.
Choose simpler words. Replace "utilize" with "use." Replace "facilitate" with "help." Replace "demonstrate" with "show." Replace "approximately" with "about." Every multi-syllable word you simplify moves your scores toward a more accessible range without losing meaning or credibility.
Use active voice. Active constructions are almost always shorter than passive ones. "The study found significant results" (5 words) versus "Significant results were found by the study" (7 words). Active voice cuts word count while maintaining clarity and improving engagement.
Break up paragraphs. Long paragraphs signal density to readers before they have read a single word. Break any paragraph longer than 4 sentences into two shorter ones. Add subheadings every 200–300 words. Visual breathing room makes even complex content feel more accessible.
Readability research began in the 1920s when psychologists first attempted to measure text difficulty objectively. The first major readability formula was developed by Linsly and Hanson in 1923, followed by Gray and Leary's comprehensive study in 1935 that identified 228 factors affecting readability — then narrowed them to four: sentence length, word frequency, personal reference density, and prepositional phrase frequency.
Rudolf Flesch published his first readability formula in 1948 while working on a PhD at Columbia University. His goal was to make government documents accessible to ordinary citizens — documents that had grown so complex during World War II that most Americans could not understand basic official communications. His formula was immediately adopted by Associated Press for training journalists to write more clearly.
In 1975, J. Peter Kincaid adapted Flesch's formula for the United States Navy to assess the readability of technical military manuals. This revision — now known as the Flesch-Kincaid Grade Level — became embedded in Microsoft Word in 1992, making it the most widely used readability metric in the world. Today it is required by law for insurance documents in several US states and is standard practice in government communication guidelines across multiple countries.