system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do 4 gallons of milk fit perfectly in a milk crate, while 9 half gallons do the same?

I was putting away half gallons of milk at the coffeeshop where I work, but we usually have full gallons. Upon realizing that 9 half gallons, or 4.5 gallons, fit in the milk crate, I wondered how that could be if 4 whole gallons of milk also fit perfectly.
gpt
I assume you're talking about plastic milk jugs?  They small ones are shaped differently than the larger ones.  The larger ones have much less volume in the upper half, due to the space cut out for the handle, while the smaller ones are a little more uniform, so the upper section contains nearly as much as the lower section.