How many cigarettes are sold in a day?

About 1 billion per day (in 2006).

According to the USDA, "Output for 2006 was 484.0 billion cigarettes...", but the consumption was 371 billion pieces for the same year. Calculating the number per day from there is simple division; 371 billion cigarettes divided by 365 days equals 1,016,438,356.16 cigarettes per day.

(see related link)