LIX Readability Calculator

LIX (lasbarhetsindex) is a readability formula created by the Swedish scholar Carl-Hugo Bjornsson in 1968. It adds two numbers: the average sentence length (total words divided by sentences) and the percentage of long words (long words times 100, divided by total words). A long word is any word of more than six letters. The result is a single index, usually running from about 20 (very easy) to 60 and above (very difficult).

A long word is any word with more than six letters, meaning seven letters or more. For example, "winter" has six letters and is not long, while "winters" has seven and is. Only letters are counted, so trailing punctuation and digits do not change a word's length. Count every long word in your sample, including repeats and proper nouns.

Lower scores are easier to read. Below 25 is very easy (children's books), 25 to 34 is easy (light fiction and magazines), 35 to 44 is standard (normal newspaper text), 45 to 54 is difficult (factual and official writing), and 55 or above is very difficult (technical and academic texts). The approximate U.S. reading grade rises with each band, from grade 5 or below up to college and beyond.

LIX measures word difficulty by letter count rather than syllables, which is what makes it language-independent. Formulas like Flesch and SMOG rely on counting syllables, a step that depends on English pronunciation rules. Because LIX only needs words, sentences, and long words, you can apply it to English, German, Swedish, or any alphabetic language and compare the results on the same scale.

Use a continuous passage rather than a sentence or two, since both sentence length and the long-word share even out over more text. A few hundred words is usually enough for a stable score. Count the words, the sentences (each period, question mark, or exclamation point ends one), and the long words, then enter all three totals.

LIX gives a single index, not a school grade, so its number is not directly comparable to a Flesch-Kincaid grade level. The two usually agree on which of two texts is harder, but the exact values differ because they weight sentence length and word difficulty differently. Use LIX when you want a quick, language-independent difficulty signal, and a grade-level formula when you need a specific U.S. school grade.