What Is Lexical Density?

Lexical density measures how much of a text is made of content words, the words that carry meaning (nouns, main verbs, adjectives, adverbs), as opposed to function words that hold sentences together (articles, pronouns, prepositions, conjunctions, auxiliary verbs). A high-density text packs a lot of information into few words; a low-density text spreads it out. Spoken English typically has lower density than written English.

The formula

The best-known version comes from Jean Ure (1971):

M. A. K. Halliday (1985) proposed an alternative: the number of lexical items per clause. It produces different numbers, so always check which method a study used.

Content words vs function words

Function words are a small, closed class of a few hundred words, but they are the most frequent words in any text (see Zipf's law).

Worked examples

Both sentences are normal English. The difference reflects their register: speech uses more pronouns, fillers and grammatical scaffolding, while formal writing compresses ideas into noun phrases (the rapid decline in coral reef health).

Typical values

Ure (1971) analyzed a range of English texts and found that spoken texts mostly had a lexical density below 40 percent, while written texts were mostly 40 percent or above. Results vary with the exact counting rules (for example, whether kind of or there counts as content), so use density to compare texts measured the same way rather than as an absolute score.

Why lexical density matters for learners

• Reading difficulty. Dense texts demand more vocabulary per sentence. A learner might read a chatty blog post comfortably and struggle with a news article on the same topic, partly because of density. The readability checker shows related measures such as Flesch-Kincaid grade.
• Academic writing. University writing usually expects higher density: The rise in temperature caused crop failure rather than Because it got hotter, the crops failed. Learning to nominalize is a key academic skill.
• Clarity. Too much density makes writing hard to follow. Plain-language guidelines effectively recommend lowering it for general audiences.

How to use it

1. Take a short paragraph of your writing and count by hand: mark every noun, main verb, adjective and adverb, then divide by the total word count. (For the related measure of word variety, use the lexical diversity calculator.)
2. Compare it with a model text of the type you want to write: a journal article, a news report, a blog post.
3. If your academic writing is much lower, try replacing clauses with noun phrases and cutting fillers. If your general writing is very high, unpack some noun phrases into verbs.

Common mistakes

• Confusing density with diversity. Density counts content words; type-token ratio counts different words.
• Treating it as a quality score. Higher is not better. The right density depends on audience and purpose.
• Comparing numbers from different methods. Ure-style percentages and Halliday-style per-clause figures are not interchangeable.

Sources: Ure, J. (1971), Lexical density and register differentiation, in Applications of Linguistics; Halliday, M. A. K. (1985), Spoken and Written Language.