Exodus 36:21 in the King James Version
The length of a board was ten cubits, and the breadth of a board one cubit and a half.
Context
20 He made the boards for the tabernacle of acacia wood, standing up.
21 Ten cubits was the length of a board, and a cubit and a half the width of each board.
22 Each board had two tenons, joined to one another. He made all the boards of the tabernacle this way.