[tdeck]

Cereal boxes are a great / terrible example of this. Have you ever noticed how many slightly different sizes of Cheerios there are?

In the U.S, you can get an 8.9oz box, a 12oz box, and an 18oz box.

Honey nut Cheerios? Oh, those come in a 10.8oz box, a 15.4oz box, or a 19.5 oz box.

You would be forgiven for thinking these boxes have remained constant over time, or that you could compare boxes between the exact same brand and class of product.

[distances]

Don't you have compulsory labeling for price per kilogram (or the US equivalent)? Of course the effect is still there, but that's the price that generally matters.

[skrtskrt]

I have never seen a US supermarket chain without it - I would imagine it's a legal req.

You're probably not going to see it in like a local corner store, but those places you know you're paying a higher price already.

[tdeck]

Not that I know of. Many supermarkets label price per ounce, but I don't know if that's a legal requirement. On the packaging all that's needed is the net weight of the item.