The Flesch Index is a metric for measuring the readability of a text. Named after its creator, Rudolph Flesch, the index is based on two main factors: the average number of syllables per word and the average number of words per sentence. The Flesch Index is a widely used tool in the fields of linguistics and education, as it provides an objective measure of the difficulty of a text.

The Flesch Index yields a score between 0 and 100, with higher scores indicating easier texts. A score of 60-70 is considered to be an acceptable level of readability for most contexts, while scores below 60 are considered to be difficult to read. The index can be applied to any text, from newspaper articles to medical literature.

To calculate the Flesch Index, the total number of syllables in the text is divided by the total number of words. This number is then multiplied by a constant (often 0.39) and subtracted from the total number of words divided by the total number of sentences. The resulting number is the Flesch Index.

The Flesch Index is a useful tool for understanding the readability of a text. It can be used to determine if a text is too difficult or too easy for a particular audience, and can also be used to compare the readability of different texts. With the increasing popularity of online communication, the Flesch Index is becoming an increasingly important tool for improving the readability of webpages, news articles, and other digital texts.


Flesch, R. (1948). A new readability yardstick. Journal Of Applied Psychology, 32(3), 221–233. https://doi.org/10.1037/h0057406

Klare, G. R. (1963). The measurement of readability. Reading Research Quarterly, 1(1), 324–343. https://doi.org/10.1598/RRQ.1.1.4

Liu, S., & Qin, J. (2015). Automatic readability assessment based on the Flesch index. In 2015 IEEE International Conference on Information and Automation (pp. 629–634). https://doi.org/10.1109/ICInfA.2015.7239099

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