LIX (abbreviation of Swedish läsbarhetsindex, "readibility index") is a readability measure indicating the difficulty of reading a text developed by Swedish scholar Carl-Hugo Björnsson. It is defined as a sum of two numbers: the average sentence length and the percentage of words of more than six letters.
Scores usually range from 20 ("very easy") to 60 ("very difficult").
The exact formula is:
, where
is the number of words,
is the number of periods (defined by period, colon or capital first letter), and
is the number of long words (more than 6 letters).
References
Further reading Björnsson, C. H. (1968). Läsbarhet. Stockholm: Liber. Björnsson, C. H. (1971). Læsbarhed. København: Gad.
External links Detailed LIX calculator (in Swedish)