Let me answer this by asking a similar question: how many pieces of spaghetti do you need to make a meal?
Obviously, there’s no answer to this.
Arguably just two pieces don’t make a full meal… but it all depends on how hungry I am. There’s no clear point where we can say “not a meal”, “now is a meal”.
Fluency in English doesn’t necessarily depend on the number of words you have memorised.
It just doesn’t work that way.
I remember this quasi-experiment I watched on Japanese TV many years ago. They sent reporters out on the street to talk to Japanese and American people. They asked the Japanese people “Can you speak English?” they would say no. When they asked the Americans (despite having had no Japanese education whatsoever) they’d reply with simple Japanese words like “konnichiwa” or “kimono”. If the only thing you need to do in Japan is to get some sushi, knowing the word “sushi” allows for a fairly fluent conversation.
But, say, you’re a sales rep for an international company. You’re going to need more vocabulary than simple words because your job depends on how you use specific words in your daily conversations.
The point is, how much you need will always depend on you and your life. The words you need to know to depend on your specific needs.
If you want to learn more about my approach to improving your English (without having to worry about pointless questions like this one) go here and sign up for the free daily English email tips I write.
Dr Julian Northbrook