John Gill Commentary Ezekiel 42:19

"He turned about to the west side, and measured five hundred reeds with the measuring reed." — Ezekiel 42:19 (ASV)

He turned about to the west side
And took the dimensions of that, from angle to angle, the south and north points of it: and measured five hundred reeds, with the measuring reed;
and it was exactly of the same measure with the other three sides.