How accurate is the estimate?

The estimate is a statistical projection, not a precise count. It assumes your known-rate within each frequency band is representative of the sample. Larger samples yield more accurate results; the 40-word quiz gives a useful approximation, typically within ±3,000 words of a longer test.

What counts as "knowing" a word?

Count a word as known if you can recognize it and roughly understand its meaning when you see it in a sentence. Do not count words you have seen but cannot define — partial recognition inflates the score.

Why do native speakers score 20,000-35,000?

Vocabulary research (Nation, 2006; Goulden et al.) estimates educated adult native speakers know 20,000-35,000 word families. Individual results vary widely based on education, reading habits, and age.

Does the quiz change each time?

Yes. Words are sampled randomly on every quiz start, so you will see a different set each time, which reduces memorization bias.

Is my data sent to a server?

No. The word lists are embedded in the page and all scoring runs in your browser. Nothing is transmitted or stored on any server.

Can I test vocabulary in other languages?

This tool currently covers English only. The frequency lists and scoring bands are calibrated for English word families.

Vocabulary Size Estimator

Name: Vocabulary Size Estimator
Availability: InStock
Author: Nham Vu

Answer known/unknown for 40 sampled words from frequency-ranked lists and get a projected total English vocabulary size.

Quiz Settings

0 / 40 answered

40 words, 4 frequency bands

Mark each word known or unknown to project your total English vocabulary size.

Start the quiz to see your projected vocabulary size.

Summary

Answer known/unknown for 40 sampled words from frequency-ranked lists and get a projected total English vocabulary size.

How it works

The tool divides a 100,000-word frequency list into bands: top 1k, 1k-5k, 5k-20k, and 20k-100k.
A random sample of 40 words is drawn across all bands, weighted toward more frequent tiers.
For each word you click "I know this" or "I do not know this."
The known rate per band is multiplied by the band size to estimate words known in that range.
All band estimates are summed to produce your projected total vocabulary size.

Use cases

Benchmark English vocabulary level before a language exam or job interview.
Track vocabulary growth over weeks of study by retaking the quiz periodically.
Compare results with native-speaker averages (typically 20,000-35,000 word families).
Identify which frequency bands need more study — high miss rates signal a gap.
Use as a warm-up exercise in ESL or EFL classrooms.
Satisfy curiosity about how your reading habits have shaped your word knowledge.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu