How to use it
- Paste English text, ideally at least 100 words, or try the example.
- Read the six scores. For Flesch Reading Ease higher is easier; the others are US school grade levels, where lower is easier.
- Check the statistics: long average sentences and many words of three or more syllables raise the scores.
- Rewrite the longest sentences listed below and watch the scores change.
How it works
All six formulas combine average sentence length with a measure of word length. Flesch Reading Ease = 206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words); 60–70 is plain English and below 30 is very difficult. Flesch–Kincaid Grade = 0.39 × (words ÷ sentences) + 11.8 × (syllables ÷ words) − 15.59. Gunning Fog = 0.4 × (words per sentence + 100 × complex words ÷ words), where complex words have three or more syllables, not counting proper nouns, hyphenated words, or words that reach three syllables only through -es, -ed or -ing. SMOG = 1.0430 × √(words of 3+ syllables × 30 ÷ sentences) + 3.1291. Coleman–Liau = 0.0588 × L − 0.296 × S − 15.8, with L letters and S sentences per 100 words. ARI = 4.71 × (characters ÷ words) + 0.5 × (words ÷ sentences) − 21.43, counting letters and digits.
Sentences end at . ! or ? followed by a space, and at paragraph breaks. Common abbreviations (Dr., e.g., etc.) and initials do not end a sentence, and neither does a full stop followed by a lowercase word. Words are runs of letters and digits; apostrophes and hyphens inside a word are kept.
Syllables are counted with spelling rules: vowel groups, minus silent endings such as -e, -es and -ed, plus vowel pairs that are usually split (as in “piano” or “create”), with a list of common exceptions. Like every automatic counter, it is sometimes off by one on individual words, but on a full text the error mostly evens out. Numbers count as one syllable.
The formulas were built for English school texts. They measure surface features only; they cannot tell whether a text is clear, accurate or well organised, and short texts give unstable results.
Examples
Writing for a general audience
A product help page scores Flesch 42 with 27 words per sentence. Splitting the three longest sentences and replacing “utilise” and “functionality” brings it to 63, in the plain English range.
Checking a policy document
An internal policy has a Gunning Fog of 17, meaning a reader needs about 17 years of education. The complex word count shows terms like “notwithstanding” and “aforementioned” to replace.
Comparing two drafts
Paste each draft in turn: the version with Flesch–Kincaid grade 8 is easier for most adult readers than the one at grade 12, which suits specialist readers.
Frequently asked questions
What is a good Flesch Reading Ease score?
For general audiences, aim for 60 or more. 60–70 is plain English that most adults read easily; 80 and above suits a wide or young audience. Academic and legal texts often score below 30.
Why do the grade-level formulas disagree?
They weigh different things: Flesch–Kincaid and SMOG use syllables, Coleman–Liau and ARI use letters, and Gunning Fog counts complex words. Each was calibrated on different texts, so differences of 1–3 grades are normal. The average is shown as a summary.
Can I use it for Turkish, German or other languages?
The numbers are calculated for any text, but they are not meaningful outside English, because the formulas' coefficients and the syllable rules are based on English. Other languages have their own formulas, such as Atesman for Turkish or Amstad for German.
How accurate is the syllable count?
It uses spelling rules plus exceptions, which gets most common words right but can be off by one on some words, such as unusual names. The effect on the final scores is usually a fraction of a grade.
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