רָב֧וּעַ הָיָ֛ה כָּפ֖וּל עָשׂ֣וּ אֶת־הַחֹ֑שֶׁן זֶ֧רֶת אָרְכּ֛וֹ וְזֶ֥רֶת רָחְבּ֖וֹ כָּפֽוּל׃
It was four-square; they made the breastplate double; a span was the length thereof, and a span the breadth thereof, being double.
Read midrashic interpretation of Exodus 39:9: and classical rabbinic exegesis.