WHAT THE RESEARCH SAYS
Nobody knows all of English. Nobody needs to.
The Oxford English Dictionary covers over 500,000 words and phrases. A large 2016 study estimated that a typical 20-year-old native speaker knows about 42,000 of the base words, and adds roughly one more every two days.
42,000 words at age 20
THE SHORT ANSWER
Count base words, word families or every form,
and you get very different numbers.
THE ESTIMATE
A 20-year-old native speaker of American English knows about 42,000 lemmas, the base forms you would look up in a dictionary, from 11,100 word families.
Count the wordsREADING
How many words people know depends partly on whether they read and watch media, because these bring far more words than conversation alone.
Grow your wordsTALK
A study that recorded 396 people found women and men both spoke about 16,000 words a day, with no real difference between them.
See the numbersWHAT COUNTS AS A WORD
Choose a measure to see the number behind it. The bar shows how large it is compared with the others.
Based on Brysbaert et al. (2016), Frontiers in Psychology, and the Oxford English Dictionary.
TWO NUMBERS WORTH KNOWING
One figure on how many words we know,
one on how fast adults keep adding them.
≈ 42,000
Lemmas known by an average 20-year-old
The estimate came from an analysis of earlier research plus an online vocabulary test taken by 221,268 people, who returned 265,346 sessions.
VOCABULARY · FRONTIERS IN PSYCHOLOGY 2016
≈ 6,000
Extra lemmas learned between ages 20 and 60
That works out at about one new lemma every two days. People also learn tens of thousands of inflected forms and names, which explains much higher counts seen elsewhere.
LIFELONG LEARNING · SAME STUDY
The study was of American English native speakers. Numbers depend on the definition of a word, the amount of language input and the person's age.
WHAT THE STUDY POINTS TO
The researchers modelled how many words people meet through conversation, television and reading. The differences are large.
Reading runs at about 220 to 300 words a minute, so a reader can meet far more words than conversation provides.
Know one member of a family and you can often understand others, as second-language research has shown.
Expressions whose meaning can't be guessed from their parts are part of vocabulary too: the average adult knows thousands.
Vocabulary keeps growing through adult life, by about 6,000 lemmas between 20 and 60 on average.
WHERE WORDS COME FROM
If people hear as many words as they speak, conversation brings about 11.7 million words a year, the study calculated. Television could bring more than twice that, about 27 million a year.
Reading can bring the most, but fewer young people read every day. In the UK, fewer than 1 in 5 (18.7%) 8 to 18 year olds said they read something daily in their free time in 2025, the National Literacy Trust found.
Questions
A 2016 study estimated that an average 20-year-old native speaker of American English knows about 42,000 lemmas, ranging from about 27,000 to 52,000.
There is no single answer, but the Oxford English Dictionary covers over 500,000 words and phrases.
Yes. The same study estimated people learn about 6,000 extra lemmas between the ages of 20 and 60, roughly one every two days.
The base form of a word, the one you would look up in a dictionary. Counts that also include inflected forms and names come out far higher, which is why published figures vary so much.
A 2007 study that sampled sounds from 396 people's voice recorders found women and men both spoke about 16,000 words a day.
Sources
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