Where these weights come from, when they are not customs
Most of the weights on this page are orders of magnitude. A handful are not, and each of them says why: the size of an egg, which is regulated; the conversion of volumes into mass; and above all the raw-to-cooked ratios of the starches, which come out of the table by dividing the energy of the raw food by that of the cooked one, the water taken up in the pot carrying no energy. That is the first trap in the arithmetic on starches: they get weighed raw and eaten cooked, and between the two the mass doubles.
Sizes S, M, L and XL come from European regulation (EC) No 589/2008: S under 53 g, M from 53 to 63 g, L from 63 to 73 g, XL above, shell included. That is a European rule and not an American one. In the United States the USDA sizes eggs by the dozen instead: Large is 24 oz per dozen, about 57 g an egg in shell, which lands inside the European M band. The shell is roughly a tenth of the egg, and the weights above have taken it off, since Ciqual measures the edible part.
The raw-to-cooked ratio is about 2.26 for white rice. It is not borrowed from custom: it comes out of the table itself, by dividing the energy of raw rice by that of cooked rice. Water taken up in the pot carries no energy, so the ratio of the energies is the ratio of the masses.
The dry-to-cooked ratio is about 2.18 for standard dry pasta, taken from the table by dividing the energy of the dry pasta by that of the cooked, the water taken up carrying no energy.
The dry-to-cooked ratio is about 2.62 for lentils, taken from the table by dividing the energy of dry lentils by that of cooked lentils. It is the highest ratio of this set: the pulse takes on more water than rice or pasta.
Volumes are converted to grams at one gram per milliliter. Beer is slightly denser than water, the gap stays under one percent, and it is smaller than the variation from one glass to the next. The two glasses above are French bar measures and not pints: a UK pint holds 568 ml and a US pint 473 ml, so neither matches the 50 cl poured here.
The drained weights are the ones printed on the common retail formats, smaller than the net weight: it is the second number on the label that gets eaten.
The 125 g ball is the standard size of the chilled aisle, and it is what sets the real portion: an opened ball keeps badly.
The one-eighth wedge is the one on retail labels, on a 250 g wheel.
Volume to mass: oil weighs slightly less than water at equal volume, so a 15 ml tablespoon holds fourteen grams. A US tablespoon holds 14.8 ml, close enough that the figure in grams does not move.
Volume to mass: honey is clearly denser than water, so a teaspoon holds seven grams where it holds five grams of water.
The cube known as no. 4 is the common size of French boxes and it weighs six grams: the most reliable measure in the cupboard, since it never overflows. A US sugar packet is lighter, around four grams, and a level teaspoon holds about five.
Baker's practice, not regulation: no rule sets the weight of a baguette, the ordinary one runs around 250 g and the tradition a little above.
The average piece of a retail tray, all formats together: maki, california and nigiri are not equal, and the average holds the range.
Volumes are converted to grams at one gram per milliliter, as for beer: the density of wine is very close to it. The two pours above are European measures; the US standard drink is 5 fl oz, about 148 ml, which sits between the two.