Lexical density: the simple ratio that measures how packed your writing is

Two passages can have the same word count, the same reading level, and the same grammar — and still feel completely different to read. One glides; the other makes you slow down and re-read. A surprising amount of that difference comes down to a single ratio: lexical density, the proportion of your words that carry meaning versus the proportion that just hold the sentence together.

It's one of the oldest measures in corpus linguistics, and one of the most useful for a self-editor, because it captures something the readability formulas miss. Flesch and Gunning Fog care about sentence length and syllables. Lexical density asks a different question: how much of every sentence is actual information?

Content words vs. function words

Every word in English does one of two jobs. Content words carry meaning — nouns, main verbs, adjectives, and most adverbs. Mountain, calculate, brittle, quickly. If you read a telegram or a search query made only of content words, you'd still understand it: "flight London Tuesday cheap".

Function words are the grammatical glue — articles, prepositions, pronouns, conjunctions, auxiliary verbs. The, of, it, and, is, to, with. On their own they mean almost nothing, but they encode the relationships between the content words. A sentence with no function words reads like a caveman; a sentence with too few content words says nothing at all.

Lexical density is simply content words ÷ total words, expressed as a percentage. A passage where 60% of the words carry meaning has a density of 60. The lexical density calculator computes this by treating a fixed list of common function words (a stopword list) as the function-word set and counting everything else as content. It's an approximation — the tool keys off a word list, not a full grammatical parse — but for comparing drafts it's both fast and remarkably stable.

What the numbers actually mean

Decades of corpus research give rough benchmarks. Casual spoken English tends to land around 40% — conversation is full of pronouns, fillers, and auxiliaries, so a smaller share of words carry meaning. Fiction and journalism sit in the 45–55% range. Academic and technical writing climbs to 55–65% or higher, because it packs noun phrases and named concepts tightly together.

The classic illustration: "I think that it would probably be a good idea if we were to go" is almost all function words — low density, and it shows. "Effective lexical compression increases information density" is nearly all content words — high density, and you feel the effort of reading it. Neither is wrong. They're tuned for different situations.

Higher is not automatically better

This is the trap. It's tempting to treat lexical density like a readability score where you chase a higher number — but density and ease pull in opposite directions. The denser the text, the harder the reader works, because there are fewer function words giving the brain breathing room between concepts. Dense prose is information-rich and tiring; loose prose is easy and slow.

So the right target depends entirely on your goal:

• Writing for a broad audience — marketing copy, help docs, news. Aim lower, roughly 45–50%. You want the reader to move quickly, and the function words are what let them.
• Writing for experts or for the record — research, specifications, reference material. Higher density (55%+) is appropriate; your readers expect concept-dense text and would find padding insulting.
• Editing a draft that feels exhausting — if your density is unusually high for the genre, that's often why. Breaking dense noun phrases into clauses with verbs and connectors lowers density and raises readability at the same time.

Lexical density vs. lexical diversity

These two get confused constantly, and they measure different things. Density is about word type — content versus function — and tells you how packed the writing is. Diversity (the type-token ratio) is about repetition — how many distinct words you use versus how often you repeat them. A text can be dense but repetitive (a technical manual hammering the same five nouns) or light but varied (a chatty essay with a wide vocabulary). For the repetition question, reach for the lexical diversity calculator instead; the two metrics are complementary, and reading them together gives a fuller picture of a text's texture than either alone.

A few practical cautions

Density is sensitive to the stopword list, so treat the exact percentage as approximate and use it for comparison, not as an absolute grade. It also varies with text length — a single sentence can swing wildly, so run it on a real passage of at least a few hundred words. And because the function-word list is language-specific, the calculator is meaningful for English and closely related languages, not for every language you might paste in.

Used the right way, lexical density is a quiet, powerful lens on your own writing. It won't tell you whether your prose is good — but it will tell you whether it's packed or loose, and whether that packing matches who you're writing for. Paste a draft into the lexical density calculator, check it against the benchmark for your genre, and adjust toward the reader you actually have.