As Mr. Wonka takes the children on the tour of his wondrous chocolate factory, he shows them his chocolate waterfall and tells them that he processes chocolate at a huge volume:
Thousands of gallons an hour, my dear children! Thousands and thousands of gallons!
We also learn that Mr. Wonka has invented more than two hundred kinds of chocolate bar, each one more delicious tasting than the last one. He employs thousands of Oompa Loompas brought in from Africa to help him produce this chocolate.
While we are not given the exact facts and figures about how much chocolate or exactly how many candy bars are produced in a month or a year, everything about the chocolate factory suggests that the delicious candy is produced on a vast scale. The chocolate bars are very popular due to their superior taste and texture, implying that many are sold. We learn, too, that Mr. Salt had his employees stop their other work and fan out to buy "hundreds of thousands" of chocolate bars in a short period of time to help insure that his daughter, Veruca, would get one of the five coveted tickets for the factory tour. This would suggest that millions of bars are put out every week.
It is ironic, given the factory's vast output, that Charlie's family can only afford to buy him one candy bar a year.