It should be obvious how twitter the company could provide a good estimate, with their server logs.
It should also be obvious how the twitter userbase has no idea, because that's exactly the problem.
So do you understand the separation now?
If not, then which part is the problem?
And you're getting downvotes because all of this was already explained, and it looks like you initially misunderstood and failed to process the reply you got and then go reread the initial post.
Oh gal, just leave a message if you downvote. I love to learn when I'm wrong, and I guess others as well.