It must be square when folded over double, a span long and a span wide.
The most considerable of the ornaments of the high priest was this breast-plate, a rich piece of cloth, curiously wrought with gold and purple, etc., two spans long and a span broad, so that, being doubled, it was a span square, Exo 28:16.
Commenting on Exodus 28:15-30
And thou shalt set in it settings of stones,.... Or "fill in it fillings of stones" (d); which shows that there were in it ouches, or sockets of gold, the hollows of which were to be filled up with precious stones: even four rows of stones; making a four square, and so filling up the measure of the breastplate: the first row shall be a...
Foursquare it shall be [being] doubled; a span [shall be] the length thereof, and a span [shall be] the breadth thereof. (i) The description of the breastplate.