Text readability indexes to optimize your site

The reading ease of your site greatly influences the users’ experience and can make a difference between a successful and a site that simply does not “work”.

The overall reading ease is not only about the typographical features of the text, which must have adequate size and form (legibility), but also about how words, phrases and paragraphs are readily recognizable (readibility).

In order to optimize your site readability, how can you objectively evaluate your texts objectively?

Here we introduce some textual measurement tools referred to as readability indexes.

Indice di Flesch

Flesh index F, valid for an English text, is calculated using the formula:

F = 206,835 – (0,864 * S) – (1,015 * P)


S is the number of syllables calculated on a sample of 100 words,
P is the average number of words per sentence.



In 1972 Roberto Vacca and Valerio Franchina proposed the following version for the Italian language:

F = 206 – (0.65 * S) – P

A second version of the same authors, proposed in 1986, is as follows:

F = 217 – (1.3 * S) – (0.6 * P)



Gulpease Index

In 1982, the GULP – a university-based linguistic pedagogical group at the Institute of Philosophy at the University of Rome ‘La Sapienza’ – defined a new formula, the GULPEASE formula, starting directly from the Italian language and testing the formula experimentally on different Reader types:

G = 89 – LP / 10 + FR * 3


LP is the number of letters per 100 / total words
FR is the number of sentences per 100 / total words

The following graph puts the Gulpease index in relation to the degree of schooling of the reader (source):


Why is the readability index important for your Conversion Rate Optimization?

A more readable text will encourage visitors to your site to continue exploring and returning, reducing bounce rates.

Consider SEO and CRO indivisible in optimizing sites we care about, so readability is in our checklist.
Let’s point out this online resource for calculating the readability of the text, currently in Italian, French and English.

Try it on your texts and please leave a comment.

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