What Size Tank Do Goldfish Need? – Goldfish Tank Size Guide

There are many myths and mis-truths in the fishkeeping world, one of the most common being: “You can keep goldfish in a bowl, because they simply grow to the size of the container.

Is this true? Can we determine what size tank goldfish need by the “fact” (in quotes because it’s not a fact) they grow to the size of their tank?

A good number of us at some point had a goldfish in a small unfiltered bowl as a kid. Maybe it was won at a fair? maybe it came from the pet store for 99 cents? It lived a year or two, often less. Eventually it died because they do that. They’re fragile creatures, and just die for no reason.

Well, that’s myth number 1: Nothing could be farther from the truth because they can live for 20 years or more!

In this article we’re going to break down these common misconceptions, take a look at what size tank goldfish need and the reasons why what we say is true. Then you’ll be able to do it right.

What size tank do goldfish need written beside a fancy goldfish in a planted tank

Myth: Goldfish Die Easily And Just Don’t Live Very Long

Many people consider goldfish delicate creatures who just up and die for no reason. In fact, they can live for decades! The healthiest, most well looked after can be expected to live for 20 or 30 years. The oldest goldfish ever recorded was claimed to be 45 years old when it died!

If treated properly, they can compete with tortoises and parrots as some of the longest lived pets you can own.

For this reason, goldfish should be considered a commitment, not an idle curiosity to keep around for a little while. There are plenty of other beautiful fish whose natural lifespan are only a few years.

Myth: Goldfish Grow To The Size Of Their Tank

Cartoon graphic of a goldfish in a cramped bowl with one large eye
© Depositphotos.com / shockfactor.de

This one is interesting. Goldfish actually do grow to the size of their tank. Anyone who’s kept one in a small bowl will testify that the fish stayed down to an inch or two.

Yet put that same fish in a 55 gallon aquarium and it could have grown upwards of a foot long! On the surface, this seems like the most accommodating fish in the world. In reality, a small bowl is stunting their growth.

Think again of our poor puppy. If it’s not allowed to run or even stand up all the way, it will become stunted and small. The kennel will be filthy and the dog will become diseased.

Similarly, the goldfish in a bowl isn’t being allowed to grow to its full potential.

They have been shown to produce a growth-inhibiting hormone when put in stressful conditions. There is debate as to why they have this ability, but experts agree it’s not a healthy thing to force them to do.

Some people even say that while the fish stops growing, their internal organs do not. They will continue to swell inside the fish, finally running out of room and causing an early death. We haven’t been able to find any hard evidence of this, but it’s as good a mental image as any to convince us to give our goldies the room they deserve.

Myth: Goldfish Can Live In A Bowl

Think of it this way. You could get a puppy and lock it up in a small kennel. Feed it twice a day and never let it out of the kennel again. The dog would likely live for years, but it would be a sad and stunted creature.

No one in their right mind would ever do this, so why would you do it to a goldfish?

This is the difference between “survive” and “thrive.”

The goldfish (or puppy in our example) can certainly survive for a time in a small and dirty environment. For the animal to truly thrive, it needs much better conditions. The puppy needs to run and play and get sunshine. The goldfish needs room to swim and clean water to live in.

Goldfish are extremely hardy creatures. They’ve been known to live for years in terribly poor conditions. Even subjected to stress, cramped quarters and filthy water, they still manage to muddle along. This is a testament to the fish, not the fishkeeper.

Just because they can survive, doesn’t mean they should be subjected to this kind of treatment.

Let’s Do It Right

We’ve learned that goldfish are hardy creatures who need plenty of space and clean water to truly thrive. So what should we do to give them the best environment possible?

Give them just that! A nice big aquarium resulting in room to freely move around and act naturally, in good quality clean water, with their environment enriched by a few decorations and plants.

Goldfish Tank Size Requirements

When it comes to taking proper care of your goldfish, tank size is one case where bigger is always better.

A 150 gallon aquarium may seem huge, but keep in mind the smallest natural ponds are many times this size. A slow flowing river may have that much water going past a fish every few seconds.

For consideration of goldfish tank size, there are two broad groups or varieties: Fancies and commons (also known as single tails).

There are plenty of differing opinions and schools of thought out there, but this is what we hold true.

The rule of thumb is as follows:

  • For fancies: 20 gallons of water for the first fish, plus 10 gallons for each additional fish.
  • For single tail varieties: 30-40 gallons of water for the first fish, plus 10 gallons per additional fish (ponds are actually best).

This may seem like a lot at first. Keep in mind though that your fancy goldfish will grow to around 8 inches, and the common single tail varieties can reach 10-12 inches. Rare cases have been recorded of commons getting even larger.

They need plenty of room to swim and forage around. The minimum length of a tank is 3 feet for fancies and 4 feet for commons.

We Also Recommend Longer And Lower Tanks

This allows for more surface area for oxygen exchange, as well as more length for the fish to swim in. A tall narrow tank might technically have the necessary volume, but wouldn’t give the fish much room to swim.

You can get away with a smaller tank when the fish is little, but you will need to upgrade soon.

In the proper environment your goldie will grow very quickly, reaching full size in approximately two years. If you wait to upgrade your aquarium until absolutely necessary, you’ve likely already stunted your fish’s growth.

So How Many Goldfish Can I Keep in an X Gallon Tank?

First of all, a couple of qualifiers:

  1. First of all,we are assuming here that the tanks being discussed are wide and shallow, not tall and thin, so the fish have plenty of room to swim around
  2. Secondly, you cannot mix fancy goldfish with single tail varieties in the same tank. The much faster swimming single tail varieties will out-compete the fancies for food, and can bully them, nip their fins and make for an unpleasant time in mixed species aquariums.

A 20 gallon tank – We do not recommend this tank size. It is too small for single tail varieties, and although this is the smallest tank in which you could theoretically keep a single a single fancy goldfish, we do not recommend keeping one alone as they are a community fish and like company. Therefore, a 30 gallon tank and at least 2 fancies is the smallest we can recommend.

A 30 gallon tank – This is the smallest size tank we would ever recommend. It is sufficient to house 2 fancy goldfish only. Although theoretically large enough to house 1 single tail, we do not recommend this as they are a community fish and keeping one alone doesn’t make for an enriched life.

A 40 gallon tank – This is large enough for:

  • 3 fancy varieties
  • 2 single tail varieties

Then, for each 10 gallons you add from here, you can add either one more fancy, or one more single tail variety. So for a 50 gallon it’s 4 fancies OR 3 single tails, for a 60 gallon it’s 5 fancies OR 4 single tails…and on and on.

If you think such large aquariums are going to be hard to maintain, fear not! Larger aquariums are actually much easier to care for than smaller ones.

The greater water volume means it will be a much more stable environment and will require less work to maintain. Imagine spilling a cup of coffee into the tank. In a 100 gallon tank, it’s a problem. In one of 10 gallons, it’s a catastrophe!

Speaking of water quality…

Water Quality

goldfish made of water jumping over slash blue water
© Depositphotos.com / merznatalia

Here’s a fun fact to tell your friends: ‘Goldfish don’t have stomachs!

They don’t actually store any food at all. Anything they eat literally goes straight through them. Because of this quirk of biology, goldfish produce A LOT of waste. They will dirty the water quickly and can easily overwhelm the biological filtration in your tank.

But the larger the aquarium you have, the less concentrated this waste will be!

Goldfish creating so much waste is also why filtration is so important in their tank. We prefer to double the amount of filtration the manufacturer recommends.

All filters sold at the live fish store will have a gallon rating on the box. If you’re keeping a 40 gallon tank with a couple of fancies in it, we recommend at least 80 gallons worth of filtration.

Like tank size, it’s almost impossible to have too much filtration. The only issue you might encounter would be too strong of a current from a canister or a hang-on-back type filter.

In addition, water changes are very important in goldfish tanks. We recommend 30-50% changes at least once a week. A good motto is, “When in doubt, change the water.

Enrich Their Environment

There is an old myth that goldfish have a 3 second memory (There’s so many myths eh?!). Supposedly they never get bored because they don’t remember they’ve seen it all before. “Hey look, a castle! Hey look, a castle! I wonder what’s over here…hey look, a castle!

In fact, it’s been shown they have a memory up to 3 months long. They even recognize faces and get to know their owners. So spice up their tank!

Add some decorations, properly cured and prepared driftwood, even some suitable plants. They will appreciate having a more interesting and engaging place to explore. This will also allow them to act and behave more naturally, foraging and investigating areas in different ways, thereby enriching their lives.

Final Thoughts On Goldfish Tank Size Requirements

So now that we’ve dispelled some of the most common myths surrounding goldfish, you should now know to NEVER to keep them in a bowl!

Make sure your goldfish have plenty of water and plenty of room by buying for them a nice, big tank, and keep that water sparkling clean.

It may seem a bit daunting at first, an expensive tank and weekly water changes but they really aren’t that expensive and once you learn a routine, it really is a simple task and the rewards of a healthy and beautiful fish are more than worth it.

Happy Fish keeping!

Wendy Kathryn

Hi, I'm Wendy, the owner and creator of this website, an experienced fish keeper and avid student of the art since 2010. My aim is to help beginners avoid the many possible mistakes when getting started in this wonderful hobby.

10 thoughts on “What Size Tank Do Goldfish Need? – Goldfish Tank Size Guide”

  1. Avatar

    Hello Wendy. I won a goldfish a couple years back and when I went to the local fish sop was told a 10 gallon tank is big enough as long as I have good filtration and change the water regularly are you saying they are wrong and I need to buy bigger they are a proper fish shop so should know what they are talking about.

    • Wendy Kathryn
      Wendy Kathryn

      Hi Yan,

      I’m afraid they are wrong, yes. There’s so much evidence and science to back up the fact goldfish need larger tanks than 10 gallons, it’s just not arguable (and is all discussed above 🙂 )


  2. Avatar

    Hi Wendy,
    What if I was ignorant for so long? Change now or leave it?
    I have three singles and one fancy in a 15 gallon tank. They have been there for 6+ years.

    • Wendy Kathryn
      Wendy Kathryn

      Hi Torrey,

      Sorry for the very late reply, I just found this in the spam comments for some reason 🙁

      I would recommend to do so, yes. It will improve your fishes life quality, and could add months or years to their life expectancy. Plus you will have more room to play around with personalising your tank too.

  3. Avatar
    Laura D Nicklas

    My friend has 3 4″Goldfish in a 46 gallon tank. The water is always cloudy. What size of tank does she need? Even after water changes. These are simple goldfish, no fancy.

    • Wendy Kathryn
      Wendy Kathryn

      Hi Laura,

      What type of goldfish are they? If single tail common varieties, they will need more room than if they are fancy varieties. Also, they may be 4″ now, but if properly looked after they will potentially grow to be much bigger than that, so she should buy a tank for the appropriate size they will be when fully grown.

      If she has 4x single tail types, she will need a minimum of 60 gallons to follow the minimum recommended guidelines.

      If she has 4x fancy types, she will require 50 gallons to follow the minimum recommended guidelines.

      As for the water being cloudy, there are a few reasons this can occur. Please see our article here: https://www.itsafishthing.com/why-is-my-fish-tank-water-cloudy/

      Hope this helps.

  4. Avatar

    i have 11 in a 40 gallon tank and they are 8 yrs old min. Kept them outside in a 55 gallon rain barrel for half of those years to eat larvae. Freeze in winter and back to life in spring. Now in basement. I don’t do water changes but I don’t clean tank algae. Filter has bio media and filters that I try not to change. Plenty of good boo slime to clean water. I consider it a natural tank. No body sees them but me. Led light on timer. They are doing great and are very happy. Feed them once a week. Sometimes longer. They are not getting bigger and some have grown long tails. All are walmart or fair fish.

    • Wendy Kathryn
      Wendy Kathryn

      I’m not looking to get into any arguments, but this is certainly not a recommended way to keep so many goldfish, Paul!

  5. Avatar

    Can send pics of you want.

  6. Avatar
    Alison barraclough

    Hi there Wendy . Just bought a new tank for my two fish was in a small tank before . They are about 6 years old , but recently since I’ve put them in a bigger tank one of the goldfish has bits of black on his fin head side etc , I went to the pets shop . With my water sample and had high nitrates and ammonia. They have been in the tank for two weeks . The other fish is fine. Pet shop lady said to leave it to settle down the water . I’m confused and don’t quite know what to do. Weather to take 30% of water out and put new in .or leave them a couple of weeks until water settles. What do you think? She also said that I could be that the fish is changing colour? Many thanks

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