Because everybody's body is different, this can vary depending on each person. Bleeding can last for up to four to six weeks after birth, so you'll want to factor in that amount of time into how many pads you'll be buying. It's also important to note you should only be wearing pads, liners, or disposable underwear after giving birth. With regular periods, you should be changing your pads every four to 8 hours. If your flow is heavy, though, you'll want to change it more frequently to every two to four hours. While you don't know how long your bleeding will last, you can assume it may be for four weeks. For four weeks worth of postpartum bleeding, with changing every four hours, you'll need a minimum of 150 pads. Any postpartum products you don't use can always be donated to those in need if you're worried about buying too many.