According to the BBC (see link below) there are 1.55 billion learners of English around the world and it’s estimated that there are 10.2 million English teachers.
How many students does that make per teacher?
Assuming an American billion (not an English one) it’s 152 students per teacher. Which seems quite a lot to me.
So 10.2 million teachers is just a few less than the number of people in London and a few more than the number of people in Chicago. Imagine a city entirely populated by English teachers. Not a single misused apostrophe in shop windows and the world’s biggest market for red pens.