"half filled" is an extremely generous description, when the contents of the breakfast cereal box are carefully engineered to be ~95% air by volume, no matter how well-settled.
(Yes, I know about Grape-Nuts, and other cereals with far higher densities.)
- A few web sites say American (breakfast) cereal boxes are roughly 12" x 8" x 2" - so 192 cu. in., or ~3,150 cu. cm.
- Similarly, the product weight for a standard box of Cap'n Crunch(tm) cereal seems to be ~12oz. - so ~340g. (Frosted Flakes(tm), Cheerios(tm), and many others look pretty close to this.)
Divide those figures, and we get ~0.11g/cu. cm.
The actual density of carbohydrates is ~1.5g/cu. cm.
So, with a generous allowance for settling, I should have said "engineered to be ~92% air by volume".
More interesting: A couple searches say that wheat, from a farmer's PoV, is currently selling for ~$5.75 per bushel. And the standard wheat bushel weighs 60 pounds. So an "all-grain" breakfast cereal should yield ~80 12-oz. boxes from that $5.75 bushel of wheat...or about 7.2 cents per box.
Far, far better to be a big corporate middle-man than an American farmer or consumer, eh?
(Yes, I know about Grape-Nuts, and other cereals with far higher densities.)