LIX measures readability using sentence length and proportion of long words (>6 letters). Works for many European languages.
Built and maintained by Paul Clark, Redmoon Software · Last verified · Sources
Use LIX when working with Germanic or Romance languages (Swedish, German, Dutch, Norwegian, Danish, Spanish, French, Italian, Portuguese). It was specifically designed not to depend on English-specific syllable patterns, so it generalises better than Flesch-family formulas.
LIX is the closest international equivalent of Flesch Reading Ease. Compared to Coleman–Liau, LIX uses word length thresholds (>6 letters) rather than averages, making it slightly less smooth but more interpretable.
LIX (Läsbarhetsindex) is a Swedish readability index created by Carl-Hugo Björnsson in 1968.
It combines average sentence length with the percentage of "long" words — words with more than 6 letters.
It generalises better to many European languages than the Flesch-family formulas, which are tuned for English.
LIX was designed for Swedish but works reasonably for Germanic and Romance languages: English, German, Dutch, Spanish, French, Italian, Portuguese.
In LIX, any word longer than 6 characters.
Scores below about 30 read as very easy, 30 to 50 as standard prose, 50 to 60 as fairly difficult, and above 60 as hard, technical text. Children's books typically sit under 30 while academic writing often exceeds 50.
LIX uses sentence length and the percentage of long words (over six letters) rather than syllables, which makes it work across many European languages. Flesch relies on syllable counts calibrated only for English.
Input
Det är en mycket lång mening med flera långa ord och tydliga underordnade satser.
Output
LIX: 39 — Medium / standard newspaper prose.
LIX combines average sentence length with the percentage of long (>6 letter) words. Most European-language news lands in the 30s–40s, and this Swedish sentence is squarely in that range.
LIX — läsbarhetsindex — was developed by Carl-Hugo Björnsson in Sweden in 1968, and its design reflects that. It counts long words as those over six characters rather than by syllable, which sidesteps the fact that syllable structure differs enormously between languages and that English-calibrated syllable rules are meaningless in German or Swedish.
The result is the one measure here that travels reasonably well. It will not give you a defensible grade level in another language, because the interpretive bands are still empirical, but the relative ordering of two documents in the same language usually holds.
LIX is not a grade level and does not pretend to be. It is an index with conventional bands: under 30 is very easy, around 40 is normal for a newspaper, 50 and above is factual or technical prose, and 60+ is difficult specialist text.
The six-character threshold is the thing to keep in mind when interpreting a result. Languages that compound heavily — German most obviously, but also technical English — cross that threshold constantly, so a high LIX on compound-heavy text is telling you about morphology as much as about difficulty.
The method behind this tool, so you can check it rather than take it on trust.
Björnsson, C.H. (1968). Läsbarhet. Liber.
The Swedish läsbarhetsindex. It travels across languages better than the English-calibrated formulas because it counts long words rather than syllables.
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