Vocabulary Size Test — How Many English Words Do You Know?

vocabulary-test.com is a free, science-based English vocabulary test that measures your vocabulary size using a two-phase adaptive methodology. Native English speakers receive an estimate in word families (typically 8,000–42,000). English learners receive a CEFR placement from A1 (Beginner) to C2 (Proficient). The test takes about 8 minutes and requires no sign-up.

How the test works

Phase i presents a recognition checklist of 32 real words and 16 plausible-but-fake decoy words. Your overclaim rate on decoys is used to correct your final estimate. Phase ii is an adaptive multiple-choice quiz: using a mathematically rigorous 2-Parameter Logistic (2PL) Item Response Theory (IRT) model, the engine dynamically selects questions that maximize Fisher Information at your estimated ability level. Using a Bayesian EAP estimator, your score updates after each response and dynamically halts the test once standard error drops below a precise threshold, typically within 15–20 questions.

Two tracks

The Native speaker track uses SAT and GRE-level vocabulary calibrated against the Brysbaert & Keuleers (2016) lexical database. The Learner track uses CEFR-aligned vocabulary across six levels: A1, A2, B1, B2, C1, and C2.

Scoring

Vocabulary size is expressed in word families. A word family includes a base word and its regular inflections and derivations. The overclaim-corrected formula ensures your score reflects genuine knowledge, not guessing. The margin of error is approximately ±3%.