687. Transporting Within a Four-Cubit Square

Shabbos 12:15

One may move objects four cubits by four cubits in the public domain within a square next to where he is standing. These are personal cubits, measured according to each person’s arm. If one has unnaturally short arms, out of proportion with his body size, he is given four standard cubits, based on the length of an average person's arm (about six feet). We have a tradition that this is the meaning of “Every person should remain in his place” (Exodus 16:29), i.e., no person should move an object outside of this square, which is based upon length of a human body with hands and feet extended.

Shabbos 12:16

If two people are near one another in the public domain and their four-cubit boxes overlap, they may each bring food into the common area and eat it together, though neither may take anything from his own exclusive area and bring it into the other’s. If three people are near one another and the middle person’s four-cubit box is enclosed within their boxes, he may share with them and they may share with him but the two people on the outside may not share with one another.