הלכה על עירובין 46:27

And since we explained the shekel-coins, it is fitting that we explain how much is a chomer: You should know that the chomer is a measure that is [also] called a kor. And a kor is two letech, and a letech is fifteen seah. It comes out that a chomer is thirty seah, which is ten eipah - as an eipah is three seah. It is a well-known thing and we also already knew it from our Rabbis, may their memory be blessed, (Eruvin 23b) that a place that has fifty ells by fifty ells is a beit seah - meaning that it is [what contains what grows from] a seah of barley - and that is two thousand five hundred [square ells] by arithmetic (multiplication). It comes out that a place that is fitting for the seed of a chomer of barley - which is thirty seah - is seventy-five thousand ells by arithmetic.