This was really frustrating when I had to be price sensitive shopping for paper towels. They'd list price per roll in the corner of the tag, but every package's rolls were significantly different cm^2 quantities.

It's a hard problem. Some stores have half-size paper towels, which I prefer, as paper towels are unnecessary large most of the time. So I want to price-compare based on number of sheets, not cm² ;)

I have the same issue with rice, they always put the price per kg, never per grain..

weight is better for rice since individual grains will vary with size and width.

That's the point, I would only take the biggests.

I only want that until someone figures it out and starts making 1/100 size sheets, or some other cheat.

I just rip off the size of paper towel I need every time I use them.

They're not half-size, though, they're actually a bit _more_ than 50%. So that means you'll go through them faster than if you purchase full-sized ones and get in the habit of tearing a full sheet in half and setting the unneeded half aside.

All of my grocery shopping is done on my supermarkets website and sorting by unit price brings up the price per pound or ounce or whatever that products unit of measure is. For paper towels it returns $ per square foot, so even if the product size is different the price per unit of measure stays the same and makes it easier to comparison shop.

It's the same for toilet paper. We really need sane regulations on packaging to make it easier for consumers.

Sometimes (at least in the UK) that number is wrong, possibly intentionally. The only really sure way is to do the calculation yourself. Unless the weight is wrong too.

I've never noticed a wrong per-price before. How wrong and what kind of wrong?

I remember shopping for kitchen roll once, one product had a per-price that was per 100 sheets, the other per roll. Impossible to decipher!

Occasionally, so wrong I actually notice. Which must be pretty wrong, because my mental arithmetic is not great.

There's also a thing they'll do where two similar products in jars/tins will have a £/kg number but one will be based on the total weight (e.g. including pickling liquid) and the other based on the weight of the actual food.

Another UK trick, promotional prices can skip showing the unit price. Tesco has turned half their prices into promotional prices. Either as multibuys or just by requiring their loyalty card to get a not insane price.

This is mandatory in Germany (probably EU)

Which is fine if the prices are given per 1 kg or 100 g. Here in the US they have the prices by the ounce or by the pound, by the gallon, quart, or liquid ounce ... not exactly transparent unless you can >> 4 in your head faster than / 10. I can't.

I usually find the numbers are (purposefully?) ridiculous.

if you compare products, one might say "3.24 per EACH" and another might say "0.04 per oz" or some other nonsense.