This page shows Calamus could not be the Measuring reed due to being only 3 1/2 feet in length.
"We all know what an inch is and what a foot and a yard is, but what is a cubit and a span and a handbreadth? We are familiar with a yardstick, a ruler and a tape measure, but people in Bible times did not use these things to measure length."
"Measuring Reed = This was an actual plant, the calamus or sweet cane which from its shape and length came to be used as a measure. See Ezekiel 40:3,5. In verse 5 the length of this reed is said to be six cubits, each of which was of the length of a cubit and a handbreadth, thus 6 cubits and 6 handbreadths (nearly 11 feet)."
Description: This perennial plant is 1–3½' tall, consisting of tufts of basal leaves that emerge directly from a spreading rootstock. These basal leaves are erect and sword-shaped, resembling the basal leaves of Iris spp. (Irises), but more green.
Sweet flag may not be a good choice for gardens visited by children and pets. This complicated plant may present varying levels of toxicity that depend largely on its variety and place of origin. The specific name calamus is derived from Greek κάλαμος (kálamos, meaning "reed")
"And behold a wall on the outside of the house round about, and in the man's hand a measuring reed of six cubits long by the cubit and an hand breadth: so he measured the breadth of the building, one reed; and the height, one reed."
"Then came he unto the gate which looketh toward the east, and went up the stairs thereof, and measured the threshold of the gate, which was one reed broad; and the other threshold of the gate, which was one reed broad."
"I saw also the height of the house round about: the foundations of the side chambers were a full reed of six great cubits."
"And the city lieth foursquare, and the length is as large as the breadth: and he measured the city with the reed, twelve thousand furlongs. The length and the breadth and the height of it are equal."
"And of this measure shalt thou measure the length of five and twenty thousand, and the breadth of ten thousand: and in it shall be the sanctuary and the most holy place."
"And the little chambers of the gate eastward were three on this side, and three on that side; they three were of one measure: and the posts had one measure on this side and on that side."
"I lifted up mine eyes again, and looked, and behold a man with a measuring line in his hand."
"And the measuring line shall yet go forth over against it upon the hill Gareb, and shall compass about to Goath."
"Now when he had made an end of measuring the inner house, he brought me forth toward the gate whose prospect is toward the east, and measured it round about."
"Acorus calamus commonly called sweet flag" Calamus is only 1–3½' tall (Bible Measurements) the Cannabis Sativa Hemp Plant is 20+' tall making Calamus too short and impossible to be the "one reed" measuring reed, Cannabis was the actual measuring reed. Example: 6 cubits converted into feet= 9 feet + 1.5 Handbreadths = 2+9= 11 feet. The measuring reed "one reed" would have had to have been 11 feet or greater and adjusted. Ir is strongly believed Cannabis was not a mistranslation as once thought, from Kaneh Bosem "many ancient languages, including Hebrew, the root "kan" had a double meaning, both hemp and reed, and that an error originated within the oldest Greek translation of the Hebrew Bible, Septuagint, in the third century B.C., where the terms "kaneh" and "kaneh-bosem" had been translated as "sweet kalamos." In the many Bible translations that followed, including Martin Luther's" also, Bible translations - Wikipedia