What Counts as "Knowing" a Word?
Vocabulary research distinguishes between several levels of word knowledge. The most commonly cited figure — the number of "word families" a person knows — counts a base word and its inflected and derived forms as one unit. For example, run, runs, ran, running, runner would count as a single word family.
Studies typically measure receptive vocabulary (words you can recognise and understand when you encounter them) rather than productive vocabulary (words you can actively use). Receptive vocabulary is consistently larger — often by 30–50%.
Average Vocabulary Size by Age
| Age | Receptive vocabulary (word families) | Notes |
|---|---|---|
| 4 years | ~5,000 | Pre-school, oral vocabulary |
| 6 years | ~6,000–10,000 | School entry; rapid growth begins |
| 8 years | ~10,000–12,000 | Reading accelerates vocabulary acquisition |
| 12 years | ~15,000–20,000 | Middle school; academic vocabulary grows |
| 18 years | ~18,000–25,000 | High school graduation |
| 25 years | ~20,000–35,000 | Average educated adult |
| 40–60 years | ~25,000–40,000 | Peak vocabulary; continues growing slowly |
Sources: Brysbaert et al. (2016), Nation (2001), Zechmeister et al. (1993).
Vocabulary Size by Education Level
Education is one of the strongest predictors of adult vocabulary size. Reading extensively — particularly literary and academic texts — is the primary mechanism through which vocabulary expands after childhood.
| Education level | Typical vocabulary range |
|---|---|
| High school (no college) | 18,000–25,000 words |
| Some college | 22,000–28,000 words |
| Bachelor's degree | 25,000–35,000 words |
| Graduate degree | 28,000–40,000 words |
| Avid reader (any level) | +5,000–10,000 above baseline |
Native vs. Non-Native Speakers
The gap between native and non-native speaker vocabulary is substantial and rarely fully closed, even with years of immersion. The Brysbaert et al. (2016) study of over 220,000 participants found that native English speakers scored an average of 27,000–29,000 word families on their online test, while non-native speakers with high proficiency averaged around 15,000–20,000.
At the C2 CEFR level, a highly proficient non-native speaker typically knows 9,000–12,000 word families — impressive, but still significantly below the native adult average. The difference lies primarily in low-frequency words: idioms, regional expressions, culturally-specific vocabulary, and rare literary terms.
The Brysbaert Study — Largest Research to Date
The most comprehensive study of English vocabulary size was conducted by Marc Brysbaert and colleagues at Ghent University. Their 2016 paper analysed data from over 220,000 participants who completed a vocabulary recognition test online. Key findings:
- Average native speaker: 27,000–29,000 word families
- Vocabulary grows at a rate of approximately 1 new word per day throughout adulthood
- Reading habits have the single largest impact on adult vocabulary size
- Men and women scored nearly identically at all ages
- The fastest vocabulary growth occurs between ages 4–18
Our test is calibrated against the Brysbaert & Keuleers corpus to ensure that scores are comparable to published research benchmarks.
What Is a "Good" Vocabulary Score?
There is no universal definition of a good vocabulary score — it depends entirely on your goals. For everyday communication, 20,000 word families is more than enough. For academic writing, you likely need 25,000+. For reading literary fiction comfortably, 30,000+ is ideal. Professional writers, academics, and avid readers typically score above 35,000.
The most important thing is not the absolute number but whether your vocabulary is growing. Adults who read regularly add approximately 300–500 new word families per year, even well into old age.
How Does Your Vocabulary Compare?
Take our free adaptive test — calibrated against the Brysbaert corpus — and find out where you stand.
Take the free vocabulary test →Frequently Asked Questions
How many words does the average American know?
Studies consistently find that average American adults know between 20,000 and 35,000 word families, with a mean around 27,000. College-educated adults typically score higher, averaging 28,000–35,000.
Do vocabulary scores decline with age?
No — unlike many cognitive abilities, vocabulary actually continues to grow throughout adulthood. Studies show that vocabulary size peaks in the 60s and 70s and only begins to decline in very old age. This makes vocabulary one of the most resilient cognitive assets.
How many words are in the English language?
The Oxford English Dictionary contains approximately 600,000 words. However, most of these are archaic, highly technical, or extremely rare. The active vocabulary of contemporary English — the words a well-read adult might plausibly encounter — is closer to 100,000–150,000 word families.