This is an old tweet, but he also mentioned this in a few talks recently.
So according to Elon Musk, Telsa is targeting to replace 1% of the total number of cars in the world every year, which is about 20m vehicles. That means you're looking at 40x revenue in 10 years. And it is relatively obvious that they are going to achieve this goal.
And that also means their forward p/e ratio is only 5 and forward p/s ratio is only 0.7 at today's price, which means the current level price would be super cheap 5-10 years from now if they can achieve their target.