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How many words does the average person know?

About 42,000. That is the median for a 20-year-old native speaker of American English in the largest study ever done, of 221,268 people; by 60 it is about 48,000. The answer depends on what you count as a word, and the more useful number is smaller: you need to know roughly 8,000 to 9,000 word families to read almost anything written in English comfortably.

By the Gloss team, PixelPaw · Published October 24, 2026 · How we check what we write

First, what counts as a word

Is run, runs, running and ran one word or four? Researchers use three units. A word form counts each spelling. A lemma counts the dictionary headword with its inflections: those four are one lemma. A word family adds the derived words: runner, rerun, runny join run. The counts below say which unit they use, because the same person “knows” 42,000 lemmas and about 11,000 word families.

The big number: 42,000

In 2016 Marc Brysbaert and colleagues at Ghent University published results from an online vocabulary test taken by 221,268 people. Each test showed a mix of real English lemmas and made-up words, and the score corrected for guessing. The median 20-year-old native speaker of American English knew about 42,000 lemmas; the 5th to 95th percentiles ran from 27,000 to 52,000. By 60 the median was about 48,200. Measured in word families, the 20-year-old knew roughly 11,100. The growth between those ages works out to about one new lemma every two days (Brysbaert, Stevens, Mandera and Keuleers, Frontiers in Psychology, 2016).

Two things follow. The range among normal adults is wide: the top of it knows nearly twice as many words as the bottom. And vocabulary does not stop at school. A person who reads keeps adding words into their sixties, roughly 180 a year without trying; a word a day about doubles that.

The useful number: 8,000 to 9,000

Knowing a word in a test is not the same as understanding a page. Paul Nation asked a different question: how large a vocabulary do you need to read and listen comfortably, which he defined as knowing 98% of the running words, about one unknown word in fifty. His answer: 8,000 to 9,000 word families for written text (novels, newspapers), and 6,000 to 7,000 for speech; about 4,000 families get you to 95%, where reading starts to feel like work (Nation, Canadian Modern Language Review, 2006). For a learner of English this is the target that matters, and it is far smaller than 42,000. For a native speaker it explains why a good novel still has a word on every other page you half-know: the last 2% is where the interesting words live.

Where the words come from

Mostly from reading. Anne Cunningham and Keith Stanovich counted rare words (words outside the 10,000 most common) per thousand in different kinds of language. Children’s books had 30.9; adult books 52.7; prime-time television 22.7; the conversation of college graduates, 17.3. Printed text is simply richer than speech, including educated speech. The same paper measured how much children read: a fifth grader at the 90th percentile read about 21 minutes a day, roughly 1.8 million words a year; one at the 10th percentile, under a minute, about 8,000 words a year, and reading volume predicted vocabulary even after controlling for general ability (Cunningham and Stanovich, American Educator, 1998). Nobody learns 42,000 words from a list. They read.

So how many do you know?

If you are an adult native speaker, probably between 27,000 and 52,000 lemmas, and more if you read a lot. The researchers’ test is online and takes a few minutes; the honest way to take it is to admit the words you only half-know. If English is your second language, the more useful question is whether you are past 8,000 word families, and the test for that is a page of a newspaper: if there is more than one word in fifty you do not know, there is still ground to cover, and it is covered by reading, with a dictionary that brings the words back.

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