Readability describes the ease with which a document can be read. Readability tests were designed to assess the suitability of books for students at particular grade levels or ages. Their primary advantage is they can serve as an early warning system to let the writer know that the writing is too dense.

There is no perfect score that applies to all websites. It depends on your target group. Google does determine the reading level of your web pages.

Obviously, readability formulas cannot measure features like interest and enjoyment. And they cannot measure whether a text is suitable for particular readers needs.

Our tool calculates three Readability scores: Fog, Flesch and Kincaid.
They all measure complexity as a function of syllables per word and words per sentence. They assume the text is well formed and logical. You could analyse a passage of nonsensical English and find the readability is quite good, provided the words are not too complex and the sentences not too long.

The Fog index, developed by Robert Gunning, is a well known and simple formula for measuring readability. The index indicates the number of years of formal education a reader of average intelligence would need to read the text once and understand that piece of writing with its word sentence workload.The Fog index, developed by Robert Gunning, is a well known and simple formula for measuring readability. The index indicates the number of years of formal education a reader of average intelligence would need to read the text once and understand that piece of writing with its word sentence workload.

   18 unreadable

   14 difficult

   12 ideal

   10 acceptable

    8 childish

The Flesch index rates text on a 100 point scale. The higher the score, the easier it is to understand the text. A score of 60 to 70 is considered to be optimal. 

The Kincaid index rates text on U.S. grade school level. So a score of 8.0 means that the document can be understood by an eighth grader. A score of 7.0 to 8.0 is considered to be optimal.