What is the Rix Readability Formula?

The Rix readability formula (often mentioned alongside a similar formula known as the Lix readability formula) is a readability formula that’s based on letter counting. Rather than being based on syllables like other formulas, Rix tackles the approach differently. Measuring readability based on syllables can be difficult in languages other than English, and both Rix and Lix are better optimized to work with foreign languages> In order to understand the Rix readability formula though, we have to take a step back to the original formula, known as Lix.

Sherice Jacob

Who Created the Lix Readability Formula?

The Lix Readability Formula  was created in Sweden by a man named Carl-Hugo Björnsson in 1968. The formula first appeared in a book called the Läsbarhetsindex which translates to “readability”. All of the writing done about the formula, which he called “Lix” for short, was done in Swedish, so it didn’t get the same level of attention or fanfare as other readability formulas like Flesch-Kincaid

How Was the Lix Readability Formula Created?

In short, Björnsson had 162 different books rated for readability by teachers and student groups. These books included everything from fiction to technical literature and textbooks. He wanted to test his formula against various criteria to determine how well it held up in tests, so he measured it against things like sentence length, sentence complexity, unusual words and much more.

Whereas other formulas count syllables and unfamiliar words, this process doesn’t extend equally to other languages. Instead, Lix calculates the percentage of words with seven or more letters. In terms of sentences the formula works similarly to Flesch-Kincaid in that it calculates the average number of words per sentence with both words and sentences being weighed equally.

So How did Lix Become Rix? 

Lix didn’t suddenly morph into Rix but it’s nevertheless important to know about Lix because of how Rix eventually developed. Rix was created over ten years later by an Australian teacher named Jonathan Anderson. Anderson wanted to take the Lix formula and adapt it to grade levels. 

In order to do so though, he had to study the validity of Rix. He did this through a variety of tests including cloze testing and determined that Lix was highly accurate. Validating the accuracy, he could now make some modifications and tweaks to help simplify the formula to a grade level designation which would in turn be simpler for teachers and librarians to understand. 

The Rix readability formula simply takes the number of words divided by the number of sentences. The ending results match up almost perfectly with Lix

Where is Rix the Most Useful?

Rix truly shines when trying to determine the readability of text for educational purposes. Because of how exhaustively they’ve been tested, both Lix and Rix are ideal for various age ranges and grade levels. They can also be used to categorize books by difficulty.

But where the Rix readability formula truly shines is in non-English texts. Whereas many readability formulas use English as their basis, Lix (and ultimately Rix) has been tested on French, German and Greek texts to name a few. This makes it an excellent formula for measuring the readability of translated texts or texts in languages other than English. 

Until recently, Lix was used primarily in the Scandinavian countries (owing to its origin there). However, with our ever more increasingly interconnected world, the Rix readability formula is starting to gain popularity in other parts of the world as well, particularly in schools that serve a large population of international students. 

Writing with Rix in Mind

If you want to use the Rix readability formula for yourself, try out Originality.AI’s new readability tool. It leverages numerous different formulas to give you a complete picture of your content readability rather than pigeon-holing your content into a single scoring mechanism. 

If you’re writing with Rix readability in mind, aim for a grade level of 8, or a Lix score of 40 or lower. You can use the Originality.AI readability checker as easily as you use the plagiarism checker or AI writing checker, and like all Originality tools, you can use them concurrently or on a case by case basis. This makes it a fast, efficient and user-friendly way to not only check work for plagiarism,  but also check for AI-written content and measure the readability of your content.

Keep in mind that Rix and Lix are best suited for non-English languages. If you want to check the readability of your content in English, there are several readability formulas you can use. Try Originality.AI’s readability checker now!

Sherice Jacob

Plagiarism Expert Sherice Jacob brings over 20 years of experience to digital marketing as a copywriter and content creator. With a finger on the pulse of AI and its developments, she works extensively with Originality.AI to help businesses and publishers get the best returns from their Content.

More From The Blog

AI Content Detector & Plagiarism Checker for Serious Content Publishers

Improve your content quality by accurately detecting duplicate content and artificially generated text.