Work out vocabulary size estimate instantly with clear inputs, formula shown and shareable results.
Vocabulary size is estimated by testing a random sample from a frequency band and scaling up. Knowing 68 of 100 words sampled from a 20,000 word band implies about 13,600 words, with a 95% interval from 11,770 to 15,430. Educated native English speakers typically know 15,000-20,000 word families.
Vocabulary estimate
estimate = (known / sampled) x band size
Confidence interval
estimate plus or minus 1.96 x sqrt(p(1-p)/n) x band size
Because a 100 word sample estimating 20,000 carries substantial sampling error. Doubling the sample narrows the interval by about 30%.
Usually recognising the meaning of the word family, not productive use. Receptive vocabulary is typically twice the productive size.