If you let products spoil, or you decide you don’t like them anymore halfway through the box, or if you forget what drawer your huge package of batteries is in, then you’re not getting as much value out of your bulk purchase as you had planned. Your effective investment return is likely to be negative; you would have been better off paying more per unit to buy less.
— Source: Buying in Bulk: When Is It a Mistake?
It’s this philosophy of “cheaper isn’t necessarily saving you money” that drove the development of Per, my little price-per-unit utility calculator. From the marketing copy:
Just because you’re getting more for your money, doesn’t mean that it’s a good buy. Maybe you’re not sure you’ve got the space to store eighty rolls of toilet paper. Or that you can get through sixteen heads of lettuce before they spoil.
Per tells you just how much more you’re getting for your money, so you can make those decisions confidently.
(I’m still planning updates for the app. Stay tuned for V2.)