Most linguists agree that there are up to a million words in the English language. It is not easy to agree on this, as a word can have many meanings. For example, there is the English word „set”, which has countless meanings in the dictionary, such as: to set, to repair, to represent, to equip, to furnish, to equip, etc...
Then there are compound words, where the combination of two completely separate words gives a third meaning. Eg: sister + hood = sisterhood.
As a rule of thumb, it can be accepted that people's passive vocabulary is twice as large as their active vocabulary. Now let's look at how many words an average native speaker knows and how many words an English language learner should know. Research shows that native speakers with a secondary school education have a vocabulary of around 20,000 words, while university graduates have a vocabulary of 40,000 words. But in fact, when they speak or write in a colloquial situation (texting, email) their vocabulary is down to 5,000 words. On this basis, if you scale your vocabulary to these 5,000 words, you will very quickly reach the vocabulary of the average native speaker used regularly every day.
Good luck!