I always thought 55 gallons. Do they need bigger? Ponds are out of the question, I'm conversation about aquariums.
i used to go by about 1 fish per gallon of river in a tank, add one gallon whether you put in gravel and decorations, and they were pretty happy and comfortable
common goldfish bring back to about two feet long (ideally)

i always hold and will continue to say that they are solely pond fish and need to be treated as such..

a fancy godfish however could be kept within a 20 gallon by it'self
2=30 gallon
3= 55 (simply because a 40 gallon will cost you as much as a 55 anyway)
Answers:    i would say a 55 is good they grow up to 2 foot but should get bigger the fancy variety grow to be 6-12"
"STUPID PEOPLE! I'm sorry. But you people drive me crazy. A goldfish cannot grow to its full size in a 10 gallon tank."

I would craft yours the best answer!
Per one Common Goldfish, you need approximately 35-40 gallons.
Wow. 55 gallons? That's insane... Buying one at a pet store when they're small (like... nearly 3 inches long) they don't need a big tank at all. Start out within like a 5 gal tank (for just one) and as the goldfish grow bigger, draw from a bigger tank. My goldfish is full size and he's in a 29 gal tank along beside his friend who is smaller. So full size for one goldfish would be about 20-25 gallons for a normal size goldfish. If you keep putting it surrounded by a bigger and bigger tank, it will grow along with the size of the tank. Mine stopped growing and he's almost... maybe 6 inches long
Ideally, 20 gallons for the first fish, next 10 for each after that.. So in a 55gallon tank you could possible save 4 goldfish.. if you keep up on tank keep.
50 gallons for the first 20 for each additional is what i recommend

but 5o gallons each is best
55 gallons? no way! i have a 7 year old goldfish contained by a 10gal

swear to god, person who gave me a thumbs down.
Im sorry, I have to say it. Those goldfish are probably half grown. Your little goldfish thats surrounded by a 10 gallon is not an adult. Maybe lifespan wise, but length he isnt anywhere close. Those goldfish would not even fit in a 10 gallon, and they arent full size but. Seriously. Your fish is going to die. Goldfish live for 15-20 years. See how long your goldfish lives.

55 gallons would be a good starts for comets and commons. You could probably put 2 in there for a touch while. Youd eventually need something like at least 150 gallons for 1. This fish will capture at least 16 inches. And likes to swim. And is very messy. So youd entail quite a large tank to house them for duration.

I agree with the guy above me that goldfish are strictly pond fish. They get the room they need within.
they need ten fish a day **
Fish floating... and tilting upwards?   Do they put on the market these at you petsmart or walmart?   Guppies too inbred? or newly adjectives happening ?   Stocking a 10g container: What else can I put within near my Betta?