Shammai says: Challah is due from one kav. But Hillel says: From two kavs. And the Sages say neither in accordance with the words of this one nor in accordance with the words of this one; rather, a kav and a half is liable to challah. And when the units were increased they said: Five revaim are subject [to challah]. R' Yose says: Five revaim are exempt, five plus are liable.