Grocery stores in the US do this, but it's not something you necessarily see in food service shops.
They do an absolute shit job of it, because there are no standards or regulations. Most times I see this, similar items next to each other on the shelf are using different "standard" units making comparison impossible (e.g. price per ounce vs. price per piece). I've even seen two sizes of the same brand/product use different "standard" units on the grocery store price label.
America is way behind Europe on this. 99% of the time I go to Safeway, I have to bring out my calculator because the reference volume/weight is different from the other items on the same shelf.
What is a bit irritating is having to recalculate when items are discounted.
You’d think it would be in their interest to display the per-unit price comparison, to emphasise where a bigger package is better value.
I know of several products that the Mid Size packaging has the best Per Unit value.
And several where they are the EXACT same price per unit, so they want to push you to the bigger one hoping you will waste most of it.
It's as often design to mislead and prevent comparison as it is to inform you that "store brand is definitely cheaper than name brand".
Since none of it is mandated, they do only what benefits their bottom line or they are publicly pressured to.
€/item, €/100g, €/1kg are all common
Maybe some German law?? Or just common practice in Germany?
Edit: I think I confused your response with parent. I understand price/kg is a thing although I didn't knew it was mandated by law. What I don't understand is being forced to use some odd unit like price per 500g.
A unit is how the product is customarily sold (singly) in the member state.
So for items typically sold as 500g in Germany, all items of that type in Germany would be labelled with 500g as the unit size for comparison. That same product may typically be sold in the UK as 1kg, so in the UK they would use 1kg.
The only time I remember having difficulty comparing was different formats of toilet paper when our usual brand was out of stock... #rolls × #sheets / pack price was a bit to much for me to do in my head. Yeah, I'm not really complaining.
This was flamboyantly repeated and amplified by the current UK Prime Minister who was then 'journalist' Boris Johnson.
There is quite literally an archive in the European Comission containing, clarifications regarding lies and misrepresentation of facts (the large majority of which created by UK newspapers).
Although packaging could be thinner, a lot of packaging is to protect from external impact/environment, and remains just as thick, but the surface area to volume ratio has increased.
If I need 3L, it’s annoying to buy 4x 750 instead of 3x 1L like I could in the past.
But the opposite can be true too: a 12 pack of soap may be 12 boxes inside a box...
The UK used to require bread to be 400g or multiples (so a regular sized loaf of bread is 800g) but it eventually got rid of that rule. Obviously years ago (this rule was hundreds of years old) it will have been some amount in an obsolete unit rather than grams, but once metrication happened the bakers picked 400g as the replacement size. I'm told it got rid of this law a few years back, but certainly last time I bought a loaf of bread it was still 800 grams.
I knew of the Bread Act that set it 1lb/2lb, and the Middle Ages origins that worked "backwards" - when the price of the loaf was fixed and the weight of the loaf was varied as the price of wheat changed.
Doesn't quite gel with modern manufacturing, though!
[0] https://www.idealo.de/preisvergleich/OffersOfProduct/354801_...
Kitchen paper towels and toilet paper can still give you a pretty good math exercise to figure out what's more affordable.
There used to be an even more drastic law proscribing certain sizes and disallowing all others. Flour would only be available in 500g and 1kg bags, for example. They got rid of it, possibly because they got sick of people making fun of EU regulations (that's what happened with the famous banana ratings)