Guide
LIX and RIX: readability that works across languages
Formulas such as Flesch–Kincaid and SMOG count syllables, and syllable rules differ from language to language, so those formulas only really work in English. LIX, developed by the Swedish educationalist Carl-Hugo Björnsson in 1968, avoids syllables altogether. It uses two features that every alphabetic language shares: how long the sentences are and how many long words they contain. That makes it the readability index of choice in Scandinavia and a practical option for German, French, Dutch, Spanish and other languages.
The LIX formula
LIX adds two numbers: the average sentence length in words, and the percentage of long words, meaning words of more than six letters. A text with 15 words per sentence and 30 % long words scores 15 + 30 = 45. Because both parts are on similar scales, sentence length and vocabulary contribute about equally.
Reading the score
The usual bands are: below 25, very easy, such as children’s books; 25–34, easy, such as popular fiction; 35–44, medium, such as newspapers; 45–54, difficult, such as official texts; and 55 or more, very difficult, such as academic, legal and technical writing. Match the band to what your readers are used to rather than aiming for the lowest possible score.
RIX and grade levels
Jonathan Anderson simplified LIX into RIX: the number of long words per sentence. He also published a table converting RIX to school grades, which the tool applies, from grade 1 below 0.2 up to college at 7.2 and above. It is a convenient way to express a score in grade terms for English texts, though the grades are approximations.
Seeing the long words
Every word of seven or more letters is highlighted in the text. In English, many are ordinary words such as “because” or “another”; the formula still counts them, which is part of why LIX works as a rough statistical measure. In revision, focus on long words that have shorter, common alternatives, and on sentences that pack several of them together.
Multilingual use
Because the formula only counts letters, words and sentences, it can be applied to any language written with an alphabet and spaces between words. Languages differ in natural word length — German and Finnish have long compounds, English many short words — so compare texts within one language. It does not work for Chinese, Japanese or Thai, which do not separate words with spaces.
A worked example
The sample paragraph about LIX itself has three sentences and about 50 words, with a high share of long words such as “developed”, “Björnsson”, “languages” and “syllable”. It lands in the difficult band — fitting for a paragraph of technical explanation. Splitting the second sentence in two and replacing a few long words lowers both parts of the score.
Comparing drafts and translations
Score the original and each revision with the same tool and settings, and look at both parts of the score: a drop from shorter sentences is different from a drop from simpler words. For translations, compare the LIX of the translation with typical texts in the target language rather than with the source text.
Related tools
Use English-specific formulas in the Readability Checker, vocabulary-based grades in the Dale–Chall Calculator, the SMOG Calculator for health information, or see sentence rhythm with the Sentence Length Analyzer.
Checked against the current version of the LIX & RIX Readability Calculator on .