Of this a square plot of five hundred by five hundred cubits shall be for the sanctuary: The demonstrative pronoun this refers to the sacred area described in verse 1. Of this may be rendered “Inside this area” (similarly Good News Translation). A square plot of five hundred by five hundred cubits is an area of ground 250 meters (840 feet) square (compare 42.16-20). This ground will be set aside for the sanctuary, that is, for the Temple compound.

With fifty cubits for an open space around it: On all four sides of the Temple compound, there will be an additional strip of land that will be left empty all around it; this was not mentioned in chapter 42. This strip of empty ground will be fifty cubits wide on each side. Fifty cubits is about 25 meters (84 feet). This means that the whole area set apart for the Temple compound will be 600 cubits (50 + 500 + 50 = 600 cubits), that is, 300 meters (1,008 feet), square. This phrase may be rendered “All around the Temple compound there will be a strip of open land that is 25 meters wide.”

Quoted with permission from Gross, Carl & Stine, Philip C. A Handbook on Ezekiel. (UBS Helps for Translators). Miami: UBS, 2016. For this and other handbooks for translators see here .