Last week I promised to research the question of the area of pe'ah (the 'corner' to be left for the poor) for a field of crops. I found the answer on this site:
There is a whole tractate of Mishnah entitled Pe'ah. It begins: 'These are the things that have no definite quantity: The corners [of the field]. First-fruits; [The offerings brought] on appearing [at the Temple on the three pilgrimage festivals]. The performance of righteous deeds; And the study of the torah.'
So, there is no prescribed size of pe'ah for a field. But that's too simple, it has to be more complex than that, right? Of course right! The passage continues: 'They should not leave peah of less than one- sixtieth [of the field]. But even though they said, “there is no measure for peah,” everything depends upon the size of the field, the
number of poor people, and the extent of the yield.'
So the final answer is ... it depends. But 1/60 is the absolute minimum gift of pe'ah. Where does this 1/60 figure come from? Mediaeval commentator R. Jacob b. Asher derives it by gematria.