Each Cubit is a forearm; as a measure of length . . . equivalent to 17.5 inches, 1.5 feet, or 0.46 meters.1 The wall measures one hundred and forty-four cubits, or approximately 216 feet (65.8 meters). Since the wall is said to be great and high (Rev. Rev. 21:12+) and the city itself is of immense height, this dimension is most likely the width.2
2 So [John MacArthur, Revelation 12-22 : The MacArthur New Testament Commentary (Chicago, IL: Moody Press, 2000)], [Monty S. Mills, Revelations: An Exegetical Study of the Revelation to John (Dallas, TX: 3E Ministries, 1987)], [Henry Morris, The Revelation Record (Wheaton, IL: Tyndale House Publishers, 1983)].