What is the Lix Readability Formula?
Lix (Swedish läsbarhetsindex, "readability index") is a readability measure developed by Swedish
scholar Carl-Hugo Björnsson in 1968. It combines average sentence length with the percentage of
long words (more than 6 letters) to produce a score from 20 (very easy) to 60 (very difficult).
Lix is language-neutral because it uses only letter counts—no syllable analysis. This makes it
effective for multiple languages, unlike formulas such as Flesch-Kincaid or SMOG that depend on
English syllable patterns.
How the Lix Formula Works
Lix uses two inputs: average sentence length (words per sentence) and the percentage of long words (more than 6 letters). The formula combines them into a score from about 20 (very easy) to 60 (very difficult). No syllables or word lists—only word length and sentence length. Because it relies on letter count, Lix works across languages and is popular in Nordic countries and in multilingual content assessment.
When to Use Lix
Use Lix when you need a language-neutral readability measure—for example for non-English text or when comparing readability across languages. It is also useful when you prefer a 20–60 scale instead of a U.S. grade level. If your audience or guideline requires Flesch-Kincaid or SMOG, use those for English; otherwise Lix is a good choice for a simple, letter-based score. To compare with all nine formulas, use our Combined Readability Checker.
Industry Guidelines and Targets
Lix is often used in education and publishing in Scandinavia and elsewhere. Lower scores (e.g. 20–35) indicate easier text; higher scores (45–60) indicate difficult text. There is no single mandated Lix target across industries, but the same principle applies: for broad accessibility, aim for a lower score by using shorter words and shorter sentences.
How to Improve Your Lix Score
To lower your Lix score (make the text easier), use shorter words (fewer words over 6 letters) and shorter sentences. Replace long words with shorter synonyms. Break long sentences into two or three shorter ones. The formula responds to both dimensions. Re-run your text after revisions to see the new score. Because Lix uses only letter count, it does not distinguish "easy" from "hard" long words—only length.
How to Use This Calculator
Paste your text into the box at the top and click analyze. You will see your Lix score and an interpretation (e.g. very easy, easy, medium, difficult). No signup required. For stable results use at least 100 words. To see how the same text scores on Flesch-Kincaid, SMOG, and seven other formulas, use the Combined Readability Checker.
Other Readability Tools
Get all nine formulas at once: Combined Readability Checker. Or explore individual calculators: Flesch-Kincaid Grade Level,
SMOG Index,
Gunning Fog Index,
Dale-Chall Readability,
Automated Readability Index,
Coleman-Liau Index,
Linsear Write,
Rix,
and the full Readability Calculators hub.
