Readability Checker: Flesch Score and Gunning Fog Index

Flesch reading ease and Gunning Fog: how the scores work

The Flesch reading ease score is 206.835 − 1.015 × (words per sentence) − 84.6 × (syllables per word), capped between 0 and 100: the higher it is, the easier the text. The tool adds the Gunning Fog index, which estimates the years of schooling needed to read the text.

How the tool works

• Words: split on spaces. Sentences: split on full stops, exclamation and question marks.
• Syllables: number of vowel groups in the word, minus one if it ends in a silent “e”.
• Complex words: 3 syllables or more.
• Flesch = 206.835 − 1.015 × words per sentence − 84.6 × syllables per word, rounded and capped at 0-100.
• Fog = 0.4 × (words per sentence + 100 × complex words ÷ words).

Reading the score: 80 and above, very easy; 60 to 79, easy (web, blogs); 40 to 59, moderate; below 40, complex.

Example

“Le chat dort sur le canapé. Il fait beau dehors et les enfants jouent dans le jardin. La maison est calme.”: 21 words, 3 sentences, 27 syllables, 1 complex word. Words per sentence: 7; syllables per word: 1.29. Flesch = 206.835 − 7.105 − 108.77 = 91 (very easy). Fog = 0.4 × (7 + 4.76) = 4.7.

Limits

• The English formula and coefficients are applied to every language. French, Spanish and German words carry more syllables, so scores are harsher: the French sample text scores 31, against about 51 with the Kandel and Moles French adaptation (207 − 1.015 × words per sentence − 73.6 × syllables per word), which the tool does not use.
• Syllable counting is approximate (diphthongs, silent letters, acronyms).
• Abbreviations and decimals create false sentence breaks.
• The score shown is Flesch reading ease, not the Flesch-Kincaid grade level.

Sources and dates: Rudolf Flesch, “A New Readability Yardstick”, Journal of Applied Psychology, 1948; Robert Gunning, The Technique of Clear Writing, 1952; Flesch and Fog formulas checked on 14/10/2026; Kandel and Moles French adaptation, 1958: indicative value, not verified

Frequently Asked Questions

What is a good Flesch reading ease score for web content?

The tool rates a text as easy from 60 and very easy from 80; 40 to 59 is moderate and below 40 is complex. For a blog post or email, aim for at least 60 with sentences averaging 12 to 18 words.

How is the Flesch reading ease score calculated?

Score = 206.835 − 1.015 × average words per sentence − 84.6 × average syllables per word, capped between 0 and 100. A 21-word text in 3 sentences with 27 syllables scores 91: short sentences and short words push the score up.

Is the Flesch score reliable for languages other than English?

The original formula is calibrated on English and the tool applies it unchanged. French, Spanish or German words have more syllables, so scores come out lower: the French sample text scores 31, against about 51 with the Kandel and Moles French adaptation. Use the score to compare versions of the same text.

What is the Gunning Fog index?

It is 0.4 × (words per sentence + percentage of words with 3 or more syllables), an estimate of the years of schooling needed to understand the text. Text for a general audience usually aims below 12; the 21-word example in 3 sentences scores 4.7.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.