How many times a day would you change the diaper of a baby in your care?
Regardless of the kind of diapers you use (reusables or disposables), it should be every 3 hours (more or less). This means 6 or 7 diapers a day which is average for a bigger baby, newborns might need slightly more (before their digestion fully develops at approx. 2 months, newborns usually poop after every feeding).
