it doesnt work that way if the rises arent all the same..... where they sit on the waist ends up being decided by the rise, the lower the rise the wider your 'waist' measurement (unless youve got a gut)
you have a 31" measurement for a 9.375", 9.75", and 10" rise. it doesnt work that way unless youre a rectangle with no curves










'Waist measurement 30 inches' shouldn't be taken as same for all jeans