Since Gustave has not been captured, his exact length and weight is unknown, but in 2002 it was stated that he could be "easily more than 18 feet (5.5 m)" long, and weigh more than 2,000 pounds (910 kg).
由於古斯塔夫從未被捕獲，牠的身長和體重數據理應不明，不過卻在2002年出現了其「身長輕鬆超過18英尺（5.5公尺），體重超過2000磅（900公斤）」的陳述。