Lol for the spring story.
I weigh my grab bags as well, of course. Maybe they use different bags in the US, but I'd guess they contain a quart (which is roughly a liter) at most, probably a bit less. Again, I usually go for the well-filled ones, and the average weight is 274 grams, which is significantly less than a pound.
Well, as others have said, it really depends on the way it is packed - whether the Lego is loose, or assembled, and what kind of bricks it is. In any way, volume is a horrible way to measure Lego.