Gauge is the thickness of the film, and it is the specification that decides whether the bag works. It is also the one most often guessed.

Start with the heaviest sale, not the average

Bags do not fail on average loads. They fail on the one heavy purchase of the day, in front of the shop, in the rain. Work from the heaviest thing a customer regularly carries out and specify to that.

If you sell bottles, that is your number. If you sell books, that is your number. If you sell clothes, your bags can be considerably lighter than you think.

Corners matter as much as weight

A boxed purchase concentrates load on four points and can puncture a film that would carry twice the weight in soft goods. If your typical sale has corners, step up a gauge or move to a bag with a bottom gusset that lets the box sit flat.

Under-specifying is expensive in public

A split bag costs you the bag, sometimes the product, and a small public humiliation outside your own shop. It is the one failure mode where the saving is invisible and the cost is not.

Over-specifying is expensive quietly

A bag twice as thick as it needs to be costs materially more per unit and no customer notices the difference. At tens of thousands of bags a year that is a genuine line item bought for nothing.

Just tell us the load

The honest short answer is that you should not have to know gauges. Tell us the heaviest thing that goes in the bag and whether it has corners, and we will specify it and say why.