Charles Ellicott Commentary Exodus 26:2

"The length of each curtain shall be eight and twenty cubits, and the breadth of each curtain four cubits: all the curtains shall have one measure." — Exodus 26:2 (ASV)

The length ... eight and twenty cubits. —Mr. Fergusson has shown that to cover over a space twenty cubits wide with a roof, the two sides of which should meet at a right angle, a tent-cloth almost exactly twenty-eight cubits long would be required.