After analyzing one million test-takers, researchers from Ghent University found that native English-speaking Americans know an average of at least 42,000 words by the time they turn 20 years old. By 60, they will know around 48,000 words.
However, don’t let that intimidate you if English is not your native language. Leading linguistic researcher Paul Nation says that “a much smaller size is needed” to read a foreign language than we are usually taught in a classroom.
In fact, according to a study conducted at Swansea University, UK, the average English vocabulary for each language level is the following:
A1: less than 1,500 words
A2: about 1,500 - 2,500 words
B1: about 2,750 - 3,250 words
B2: about 3,250 - 3,750 words
C1: about 3,750 - 4,500 words
C2: about 4,500 - 5,000 words