Design ease and wearing ease are necessary for garments. That said, at least 1-1.5 " in the waistband is the average for wearing ease. Also that depends on where the waistband is designed to sit on the body. Low rise jeans have a larger waistband than high rise jeans just by nature of where the band sits. This has a lot to do with the fact ready-to-wear clothing sucks at fitting the diverse range of bodies out there.