A newborn baby uses between 6 to 10 diapers per day and sometimes can go through 14 diapers per day during the first month or two of the newborns life.
As the baby gets older they tend to wet and poop less often so they will usually go through less diapers.
But just to be safe you should have at least 10 diapers per day on hand because it's always better to have more diapers than you need.