Coptodon rendalli grow to a maximum length of 45 centimeters, reach a maximum weight of 2.5 kilograms, and possess a high-backed, sideways oblate body. Their body height is 42.2 to 49.4% of their standard length, their head length is 31.1% to 37.5% of their standard length. The top of their head is convex, it sometimes will be concave in large specimen due to the continued growth of their mouth region.