u/RevolutionaryLove134

It takes about 1,500 words to gain one IELTS band, at least all the way to the C1 level (IELTS 7.0).

It gets much harder after that once we are getting deeper into C1 and toward C2 territory. To gain an IELTS band by going from mid-C1 (IELTS 7.5, 8,400 words) to C2 (IELTS 8.5, 13,100 words), one needs to learn 4,700 new words - 3 times more than for the bands before.

About the BRAVE test: it measures receptive vocabulary (words we understand, but do not necessarily use). The results are in word families (limit, limitation, limitless, etc., are counted as a single family). I made BRAVE and collected the data from people all over the world, with a good share coming from Reddit. I am sharing the results with the English learning community.