LIX (Läsbarhetsindex) is a readability index created by Swedish researcher Carl-Hugo Björnsson for the Swedish language. Unlike syllable-based formulas, it was designed to be easy to compute by hand and works across languages because it relies only on word length and sentence length.
How it works
LIX uses three counts: total words, total sentences, and the number of long words. A long word is any word with more than six letters (seven characters or more). The score combines average sentence length with the percentage of long words:
LIX = (words ÷ sentences) + (longWords × 100 ÷ words)The first term is the average number of words per sentence. The second term is the share of long words expressed as a percentage. Adding them produces a single index that rises as sentences get longer and as more long words appear.
Why LIX was built for Swedish — and why it works in other languages too
Swedish forms long compound nouns naturally — barnuppfostran (child-rearing), sjukvårdsförsäkring (health insurance), inkomstbasbelopp (income base amount). Syllable-based formulas like Flesch are tricky to apply reliably across languages and require language-specific calibration. LIX sidesteps this by counting letters rather than syllables, making it language-neutral in practice, even though it was designed for Swedish.
LIX reference bands
| LIX score | Text type | Typical audience |
|---|---|---|
| Below 25 | Very easy | Early children’s books |
| 25–30 | Easy | Older children’s fiction |
| 30–40 | Medium | Newspaper prose, general web |
| 40–50 | Difficult | Factual, official, technical |
| 50–60 | Very difficult | Academic articles |
| Above 60 | Extremely difficult | Legal/legislative text |
For Swedish web content aimed at a general audience, aim for a LIX score below 40.
Worked example
Consider this sentence (translated for illustration): “The annual income ceiling that determines the pensionable income in the Swedish public pension system is set at seven-and-a-half income base amounts.” This single 23-word sentence contains several long compound words. Its LIX contribution from sentence length alone is 23; the long-word percentage adds further. A passage of such sentences would score in the 50–60 range.
By contrast, a short news lead — “Sweden raised the minimum wage. Unions agreed to the change.” — averages 7 words per sentence with few long words, producing a LIX below 30.
How to reduce your LIX score
- Shorten sentences first. The average sentence length is added directly to the score, so splitting one long clause into two is the single most effective improvement.
- Break up compound nouns. Swedish allows compounds of arbitrary length; where meaning permits, use a shorter synonym or rephrase.
- Active voice. Passive constructions often require longer verb phrases that add long words.
- Re-check live. Paste your revised text and watch the score update in real time.
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