How many pads/tampons a woman uses depends on her flow. A period can last anywhere from 2-7 days, give or take. Heavy flow days can require a pad every couple hours, more or less, where as a light day could only require one pad for the whole day. Tampons are different because they have to be changed regularly, having them in for no more than 8 hours because of TSS. Additionally, some women wear a pad with their tampon in case the tampon leaks, which could contribute to costs.