Goldfish can grow quite large depending on their breed and environment. Typically, common goldfish can reach around 12 to 18 inches (30 to 45 cm) in length, with fancy goldfish usually being smaller, around 6 to 8 inches (15 to 20 cm). Some record-size goldfish have grown to about 15 to 19 inches (38 to 48 cm) and weigh up to 9 pounds (4 kg) in large ponds or lakes. Growth is influenced greatly by tank or pond size and water quality, with goldfish never truly stopping growing as long as conditions allow.