Produce? Priced per pound (usually). BUT the comparison price is per kg for some reason? Except not always?
Liquid? Per 100ml, except for the one specific thing you want to compare, which is measured per volume of a size 10 sneaker.
Dry goods? Per 100g or kg (or rarely, pounds) with no rhyme or reason as to which they choose.
Toilet paper? Compare "sheet", which will require a terminal degree in advanced mathematics to calculate (one roll of SUPER PLUSH is equal to 7.2 rolls of MEGA PLUSH, which is 4.875 of double, which is anything except twice as many as).
In Canada, we actually have a big colourful wheel that Chrystia Freeland spins to decide what unit we use when measuring a specific thing.
Experiencing this all the time in the US. Want to buy extra virgin olive oil? One is priced in "per floz" another in "per quart" and a third in "per pound". All three contain same EVOO in the same size range (500mL-1000mL) on the same shelf. How many ounces are in a quart? Is a fluid ounce the same as a dry ounce? Fuck you! Hope you are skilled at multiplying by 16 in your head. I swear the grocery stores do this on purpose to protest the fair pricing law that forces them to display the unit price. If it were left up to random chance alone, the units would match at least some of the time. EVOO is the reason I hate the imperial measures system.
In my country its a law that the "price per weight" has to be on the tag. It may vary which unit they are using but with the metric system its just a matter of moving the comma.
I use the "price per" information quite a bit when shopping, but it's kind of infuriating that units can often be different, even for the same type of item.
Some produce is priced per lb, and others are per kg, and others per oz, and others per 100g.
What's really weird is that sometimes they'll print the wrong style of label, e.g. video games with a grocery label, so now you get to see how much Mario Kart 8 Deluxe costs per pound.
If my local supermarket is any indication those $/oz (or per 100ml in my case) are entered manually by employees and can be wildly inaccurate.
So maybe double-check them.