alt Hacker News> which is pretty exactly a cubic meter
That would be if we were talking about water (and at 4ºC if we want to be "exact"), but potatoes have a different density and cannot fill the space entirely due to their irregular shapes. Are you saying that those two things cancel themselves out and the result is that 1 cubic meter of potatoes is "exactly" 1 tone?
Pretty much. See the FAQ here https://4000-tonnen.de/faq.html
> Wie werden die Kartoffeln geliefert? Die Kartoffeln werden per LKW direkt an Ihre angegebene Adresse geliefert. Die Lieferung erfolgt in einem Big Bag, in das ca. 1000 Kilogramm Kartoffeln passen.
Standard Big bags are roughly 1x1x1m