Readability index
Paste a text and the readability index is worked out, along with the figures behind it.
Paste a text above.
The scale
- Below 30 – very easy, like children’s books
- 30–40 – easy fiction
- 40–50 – ordinary prose, such as newspapers
- 50–60 – hard, often specialist writing
- Above 60 – very hard, bureaucratic or academic
A long word has more than six letters. Punctuation does not count towards word length.
How it works
LIX is a readability measure developed by Carl-Hugo Björnsson in the 1960s. It is the mean sentence length plus the percentage of long words, where a long word has more than six letters.
It measures two things that both make a text heavier: long sentences, which ask the reader to hold more in mind, and long words, which are often compounds or technical terms.
Below 30 counts as very easy, like children’s books. 30 to 40 is easy fiction, 40 to 50 ordinary prose such as newspapers, 50 to 60 is hard, and above 60 is bureaucratic or academic writing. The bands are a rule of thumb with no established source, and they were set for Swedish. When Björnsson compared newspapers in eleven languages, Swedish papers came out at 47, German at 59 and Finnish at 72, so the same kind of text lands differently from one language to the next.
A low score is not a goal in itself. What matters is the reader: a text for the general public should sit low for its language, while a technical report for specialists may sit higher.
The measure looks only at length, not at meaning. A text full of short but impenetrable words still scores low, and a well-written text with a few long proper nouns scores higher than it deserves.
Sentences are counted from closing punctuation, so abbreviations with full stops can register as sentence ends. The value is an estimate, not an exact measurement.
The same message, three ways
Three versions of roughly the same message about an application, written for this page. LIX is worked out with the tool above.
| Text | LIX | Level |
|---|---|---|
| PlainWe have your application. We are reading it now. You will hear from us within two weeks. Call us if you have questions. | 19 | Very easy |
| Ordinary proseThank you for your application, which we have received and registered. Processing normally takes about two weeks, and once a decision has been made we will send it in writing to the address you gave us. Contact your caseworker if you have questions or need to add anything. | 41 | Ordinary prose |
| OfficialeseYour application has been received and is undergoing consideration, whereupon a determination is anticipated within an administrative period of approximately fourteen days. Any enquiries concerning the aforementioned matter should be directed to the responsible administrative officer. | 65 | Very hard |
How LIX is worked out for the first text
- The text has 23 words in 4 sentences, so 5.8 words per sentence on average.
- The number of long words, meaning words with more than six letters, is 3. That is 13.0 per cent of all the words.
- LIX is the sum of the two figures: 18.8.
The formula
LIX is the number of words divided by the number of sentences, plus the number of long words times a hundred divided by the number of words. The first part measures sentence length and the second the share of long words. A long word has more than six letters. Punctuation does not count as letters, and a figure counts as a word but never as a long one.
Carl-Hugo Björnsson published a study of readability in Swedish school books in 1964 and the book Läsbarhet in 1968. Because it only counts letters and words it works in other languages too, and it is used in several European countries, but the bands for easy and hard were set for Swedish text. When Björnsson compared newspapers in eleven languages, Swedish papers scored 47, German 59 and Finnish 72.
Plain language
Plain language guidance exists in most countries: in the United Kingdom through the Government Digital Service style guide, in the United States through the Plain Writing Act of 2010 and the federal plain language guidelines on digital.gov, and in Sweden through the Language Act, which requires public bodies to write in language that is cultivated, simple and comprehensible.
Plain language is more than short words and sentences. It is about leading with what matters, addressing the reader directly, using active verbs and explaining technical terms. LIX measures only part of that, and a text can score low and still be hard to follow.
Other readability measures
For English the Flesch reading ease score, published by Rudolf Flesch in 1948, is the most widely used. It counts syllables per word rather than letters, and a high score means an easy text, the opposite of LIX. Flesch–Kincaid, developed for the US Navy in 1975, weights the same two figures differently and reports a US school grade level.
Counting syllables is awkward outside English, and LIX avoids it by counting letters. That is one reason it travelled to other languages, although the bands still reflect Swedish text.