en_tn_condensed/jer/52/21.md

eighteen cubits ... twelve cubits

A cubit was about 46 centimeters long. Alternate translation: "18 cubits ... 12 cubits" or "about 8.3 meters ... about 5.5 meters" (See: rc://en/ta/man/translate/translate-bdistance)

hollow

The pillars had empty space inside them.