Readability Checker
Paste any text to instantly calculate four widely used readability scores — Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog Index, and Coleman-Liau Index. Useful for writers, teachers, content marketers, and anyone who wants to make sure their writing reaches its intended audience.
Words
Sentences
Syllables
Avg Words/Sentence
Flesch Reading Ease
Flesch-Kincaid Grade Level
US school grade required to understand this text. Grade 8 = 8th grade (age ~14). Most popular fiction targets Grade 6–8.
Gunning Fog Index
Years of education needed to understand on first reading. Scores above 12 are considered difficult. Business writing aims for 10–12.
Coleman-Liau Index
Estimates US grade level based on characters per word rather than syllables. Less sensitive to syllable-counting errors.
Understanding the Readability Scores
Flesch Reading Ease
The Flesch Reading Ease score, developed by Rudolf Flesch in 1948 and later refined by the US Navy, produces a score on a scale from 0 to 100. Higher scores indicate easier text. The formula penalises both long words (measured in syllables) and long sentences:
FRE = 206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words)
| Score | Difficulty | Comparable to |
|---|---|---|
| 90–100 | Very easy | Children's books |
| 80–90 | Easy | Conversational English |
| 70–80 | Fairly easy | News, consumer-facing content |
| 60–70 | Standard | Popular fiction, most websites |
| 50–60 | Fairly difficult | Business reports, quality newspapers |
| 30–50 | Difficult | Academic journals, legal documents |
| 0–30 | Very difficult | Professional / scientific papers |
Flesch-Kincaid Grade Level
The Flesch-Kincaid Grade Level converts the same underlying data into US school grade equivalents. A score of 8.0 means an 8th-grade student (approximately 14 years old) should be able to understand the text. The formula is:
FKGL = 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59
Most popular fiction (Harry Potter, The Hunger Games) tests at Grade 5–7. The New York Times averages around Grade 10–11. Scientific papers often exceed Grade 16.
Gunning Fog Index
Developed by Robert Gunning in 1952, the Fog Index measures how many years of education a reader would need to understand a passage on the first reading. It identifies "complex words" as words with three or more syllables (excluding proper nouns, compound adjectives, and verb forms made three syllables by suffixes like -ed or -es):
Fog = 0.4 × [(words ÷ sentences) + 100 × (complex words ÷ words)]
A Fog score of 12 corresponds to US high school senior level. Scores under 8 are ideal for broad public audiences. Time magazine targets a Fog score of around 11.
Coleman-Liau Index
Unlike the other formulas, Coleman-Liau does not count syllables — it uses characters per word and sentences per 100 words. This approach is more robust because characters are easier to count programmatically and because syllable counting in English is notoriously imprecise:
CLI = 0.0588 × L − 0.296 × S − 15.8
Where L is the average number of letters per 100 words, and S is the average number of sentences per 100 words. Results are expressed as US grade levels, similar to Flesch-Kincaid Grade Level.
What Readability Score Should Your Writing Target?
The right readability level depends on your audience:
- General public / consumer marketing: Flesch 60–70, Grade 6–8. Most adults read at or below an 8th-grade level in everyday contexts even if their formal education is much higher.
- Business writing: Flesch 50–60, Grade 10–12. Reports, memos, and proposals can be slightly more complex if the audience is professional.
- Healthcare and patient education: Flesch 70+ is strongly recommended. The US National Institutes of Health recommends that patient-facing materials target a 6th-grade reading level.
- Legal documents: There is no universal standard, but the plain language movement in the US and UK pushes for Flesch 40–50 in consumer contracts.
- Academic and scientific: Grade 14–20+ is normal. Audience expertise compensates for complexity.
To see how your reading time correlates with the complexity level, use the reading time calculator alongside this tool.
Frequently Asked Questions
Why might the scores differ significantly from each other?
Each formula weights different factors. Flesch Reading Ease and FKGL emphasise syllable density. Gunning Fog focuses on long words (3+ syllables). Coleman-Liau uses character counts. A text with many short but multi-syllable words (like scientific jargon) will score very differently across the formulas compared to a text with long sentences made of short words.
Is there a minimum text length?
Readability formulas are statistical and become unreliable for very short texts — a single sentence or a headline can produce wildly misleading scores. Aim for at least 100 words for a stable result; 300+ words is ideal.
Do these scores work for languages other than English?
The formulas were calibrated on English text. Syllable-counting heuristics are language-specific, and word/sentence length norms differ across languages. Results for non-English text will be systematically off. There are localised readability formulas for several languages (e.g., Lix in Scandinavia, Wiener Sachtextformel for German).
Can readability scores tell me if my writing is good?
Not directly. A low score means text is harder to decode — longer words, longer sentences — but not necessarily poorly written. Kafka, legal contracts, and medical textbooks all score "hard" by design. Readability scores are a diagnostic tool, not a quality judgment. That said, for most public-facing writing, simpler is usually better. For more text statistics including word count, try the word counter.
