There are a range of formulae that can be used to assess the readability of written text.  While these all have limitations, judicious use of several ‘readability' predictors can improve the clarity of writing of articles, theses, reports and assignments.

The software used here, an online readability calculator, will return a number of indicators including the average words per sentence, Fog index, Flesch reading ease score, and Flesch-Kincaid grade level. These readability indicators may be of help in editing and developing your written work.

It is unclear how useful computer programmes are for analysing scientific writing since the language used tends to be complex. However, some studies have shown that the indicators derived using the software here do have value.

The average words per sentence is a crude measure of readability. If your average sentence length is more than 22 words it is likely that there your writing is not clear; there may be too much detail or content. If the word length is less than 14 then your text may also be difficult to read; the ideas may appear broken up and discontinuous. However, if the word average appears around 14-22 there may still be a problem since variety in sentence length is also required if text is to be readable.

The Fog index is a well known 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. The values shown below indicate the numerical scores associated with text described as childish through to unreadable.

18 unreadable
14 difficult
12 ideal
10 acceptable
8 childish

The Flesch reading ease score,considers number of the syllables per word and the average word length of sentences to assess readability using 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 Flesch-Kincaid grade level score returns the U.S. grade level score for the analysed text file or block. It also uses an analysis of the number of syllables and average sentence length to generate a grade. A score of 7 means that the text can be understood by U.S. seventh grader. A score of 7.0 to 8.0 is considered to be optimal.

For those wishing more information on this subject there is a useful article in Wikipedia and an  On Line readability software development group lead by Dave Child  that may be helpful.


Use the calculator

How to cite this article

Mullan, W.M.A. (2008). [On-line]. Available from: . Accessed: 14 April, 2024.