average t rex size
edit Size. T. Rex adults were a significantly larger compared with allosaurus adults. An allosaurus adult was between 8.5 and 12m in length (28-39 ft), while the average T. Rex adult was about 12-15m long (40-50 ft). The average height of an allosaurus was 17ft (a little over 5m) while T. Rex was about 23ft (7m) tall on average. The T. Rex was also substantially heavier at 14,000 lbs compared to the allosaurus at 4,000 lbs.