83:2 The area of two seah (referenced in the previous halacha) is the size of the courtyard of the Mishkan; it is 100 cubits long by 50 cubits wide. (A cubit is about 18 inches, so we’re looking at about 150 feet by 75 feet.) If the area is square rather than rectangular, it would be about 70 cubits and 4 handbreadths on each side. (The Kitzur Shulchan Aruch says that’s a little more than 53 meters.) If the area is round or any other shape, an area of 5,000 square cubits must be estimated. (The Kitzur provides an equivalent of 3,750 meters.) If the length of the area is more than twice its width, even by a single cubit, it is considered like an area greater than two seah because it is no longer like the courtyard of the Mishkan. (If the length exceeds twice the width by less than a handbreadth, it is of no consequence – Mishnah Brurah 358:12. If the total area is less than 5,000 square cubits, it makes no difference how long and thin the area might be – ibid.)
83:3 If an area has been enclosed not to serve a dwelling and is not larger than two seah, one is permitted to carry in it. If there is a courtyard adjacent to it, one may also carry from this area to the courtyard and vice versa (even if they belong to two different people who have not joined through an eiruv – OC 372:1). This only applies to items that were already in the enclosed area or the courtyard when Shabbos began because these are considered a single domain. The enclosed area does not share a common domain with the house so items may not be transported between the area and the house or vice versa.