The key to understanding how to intelligently buy trash bags is this: the wholesale market is priced using cost-per-pound (of plastic) and the typical retail or institutional buyer is focused on cost-per-bag. So any solution which allows you to reduce the amount of plastic per bag (without creating a weak bag) can be a cost savings opportunity. Potential options: select the right trash bag size, buy thinner bags, or shift non-sharp / wet trash from low density to high density bags.
This calculator gives you an idea of how much plastic should be in the box for a given bag specification. Plastics reduction should translate to a direct reduction in case cost, regardless of the number of bags delivered. Numbers presented is net weight - the weight of the packaging (cardboard box) shouldn't be included.
This tool also gives you a way to spot when your suppliers are playing games with the specifications and shipping you a light box. Speaking as someone who has run pricing for honest manufacturers (we don't cheat on specifications), these cheaters are a pain in the neck to bid against. So go ahead - weigh a box and see if the math matches!
For those of you "in the business", we've included a handy can liner pricing tool which allows you to take your cost-per-pound for that grade and apply an appropriate mark-up percentage. This will give you an estimated case cost and resale price for the case of can liners. In the event the estimated weight differs from the typical case weight, the calculator has two ways to true this up. First, if you know the resin your manufacturer uses runs X% light, enter that as an adjustment in the weight adjustment (for example, 96% if the typical case weight for that manufacturer/grade runs 4% below the formula). Alternatively, you can enter the actual case weight from their catalog (recommended).