How fast do goldfish grow?

Goldfish can get VERY big. Actually, they naturally never stop growing. They can even get up to 3 feet. You may find this hard to believe, but this is because most goldfish's growths are stunted because of small tanks. Sometimes they adapt to the tank size and only grow if put in a bigger tank but this is rare. If a goldfish is given a healthy, natural life, they will continue to live and grow. The record for oldest fish is about 49 years.

The person above me is very right. Goldfish usually don't reach their full length because they die (cuz of small tanks, over feeding, and any other abuse) before they can. They never stop growing but their growing starts to slow down after a while. That's why it's 20 gallons for one goldfish and another 10 gallons for additional goldfish (3 large fancy goldfish in a 50 gal).

The two people above me are partially right. There is no record of any goldfish reaching 3 feet, only koi can attain a length that big. Goldfish are also capable of growing to their adult size (12 - 14 inches) in a 10 gallon tank as long as you keep the tank clean, warm and you put the goldfish on a varied diet. Although, since goldfish can grow big and produce a lot of waste, it is best that you move them to a bigger tank once they grow-out their old one.

According to experts, an ordinary or common goldfish will grow up to 26 inches while koi carps will grow and weigh up to 90 lbs.

REALLY REALLY BIG, of course depending on the tank size, if put in a big tank they can reach the size of a koi

They can live to the age of 45 if in clean conditions. They can get as large as 10'', but if they have descendants of a large fish such as a koi it can grow as large as a koi. The goldfish also grows with the tank as you give it bigger ones. I have a comet goldfish who is half that has lots of koi in him and a little bit of goldfish,he is 2 years old.
It will grow to the size of the tank you might have you see the big gold fish in the shop what r about 5-7 ich long