How many people smoke worldwide?

How to get close to this number

Apply a prevalence rate to the adult population. The explanation gives it as roughly one in five people over fifteen, and the world holds around six billion people in that age range. A fifth of six billion gives the answer directly, and prevalence times population is the standard epidemiological route.

The trend is the counterintuitive part: the absolute number has fallen for a decade even while world population grew, which means prevalence has dropped faster than population has risen. That is a genuine public health success, and it is rare enough that it deserves stating rather than being buried under the mortality figure.

The mortality comparison is the one that gives the number weight: tobacco kills more people annually than malaria, tuberculosis and HIV combined. Those three diseases receive the overwhelming majority of global health attention and funding, and the largest single preventable cause of death is a consumer product sold legally almost everywhere.