Ramar's height fluctuates throughout the entire mini-series. When Duke first confronts Ramar in the Arena of Sport, Ramar towers over him, and looks to be somewhere between 13-14 feet tall (if we are to believe Scarlett's line that Duke is 6'2"). In the second episode, in close quarter combat with Duke, Ramar looks to be a couple of feet taller than Duke, which would place him in the 8-9 foot range. By the fourth episode, Ramar stands next to Selena and is barely taller than she is, which would make him somewhere between 6-7 feet tall.
At the end of the first cliffhanger, Ramar the Giant Slave swings his arms and knocks down two stone columns (a preposterous notion in and of itself); as the second episode opens, a large overhead shot now shows the two columns that he knocked down about 50 yards apart. In order to knock them down, Ramar would have needed a wingspan of about 150-160 feet!