I plan to make a BIG pot of onion gravy soon. Is there a rule of thumb about the volume and weight relation of sliced onions?
So, my big pot holds about 12l - I’d go for 10l here to have room to stir - if thinly sliced on a mandolin, how many kilograms of onions would that be?
Or, the other way round, if one slices a kilogram of onions, how much volume would that fill?
So this obscure research paper gives the density of onion at 0.86kg/l, while this online calculator has it at 0.55kg/l for cubed (!) onion. The latter is probably the better guide if you slice them. So for 10l, I would probably buy something like 6-8kg, see what fits in the pot and use the rest for something else.
The 0.86kg/l is basically the same as many other veg and fruit, and everyone who had ever placed an onion in water would not be surprised that it floats.
The 0.55kg/l for the cubed onion probably depends on the size of the cubes; especially if they are smaller, there would be a lot of compression with the pot being nearly 40cm high, rapidly approaching the 0.86kg/l mark, at least at the bottom.
I think the 6-8kg is a good and reasonable approach based on that data; I’ll need some more onions for two other dishes, so leftovers will not go wasted. Although I need them with vastly different cuts. But the question is more about the amount to buy and peel, the distribution among the dishes can be done rather simply.