Do goldfish need a big tank? Why goldfish tank size matters

Goldfish tank size is really important! In fact, the goldfish tank size you choose when you first buy your fish is one of the most important decisions you’ll make while caring for your fish.

The reason that goldfish tank size matters so much is that goldfish need a big tank. Much bigger than most people think!

You see, as well as thinking about the current size of your fish, you need to think about the potential size of your fish too. This is because you don’t just have to give your goldfish enough room for today. You need to give them room to grow.

It’s important to realize that the goldfish you buy from a pet store are very young. They haven’t yet reached anything close to their full adult size. And you might be surprised to learn just how big goldfish get

Common goldfish can easily reach 10 inches and fancy goldfish regularly reach 8 inches in length.

Imagine trying to fit an 8-10″ fish into a goldfish bowl! It just wouldn’t work. Your fish would suffer and it wouldn’t live very long at all. That’s why you need to give your goldfish a nice big tank or pond.

What goldfish tank size do I need?

The goldfish tank size you choose will depend on whether you have a fast-swimming, slim-bodied fish, like a Common, Comet or Shubunkin goldfish, or a slower-swimming fancy goldfish.

Common and Comet goldfish tank size

For Common goldfish, Comets and Shubunkins, we recommend a tank measuring at least 4 feet long with a volume of at least 30 gallons. Of course, it’s a case of the bigger the better! So any more than this is great too.

If you plan to keep more than one goldfish in your tank then add an extra 12 gallons for each additional fish.

While it is certainly possible to keep Common and Comet goldfish in a tank, they can grow so large – and are so fast swimming – that they are really better suited to living in a pond.

Fancy goldfish tank size

For fancy goldfish, we recommend a tank measuring at least 3 feet long with a volume of at least 20 gallons.

If you plan to keep more than one goldfish in your tank then add an extra 10 gallons for each additional fish.

What if I have two goldfish?

Based on the rules above, the goldfish tank size we recommend for two goldfish is:

  • 42 gallons for two Common goldfish. That’s 30 gallons for the first fish and 12 additional gallons for the second fish.
  • 30 gallons for two fancy goldfish. That’s 20 gallons for the first fish and 10 additional gallons for the second fish.

You might have noticed that 30 gallons is the recommended figure for a single Common goldfish or for two fancy goldfish. If you have a 30 gallon tank and are thinking about which goldfish to buy, this might help you make your choice!

What if I have more than two goldfish?

You can, of course, use the rules above to work out the goldfish tank size you will need for any number of goldfish. However, in most cases, you’ll find that keeping more than two goldfish is impractical. The majority of people simply don’t have enough space for the tank size that would be need for that number of goldfish.

For example, even three common goldfish would need a tank size of 54 gallons (30 gallons + 12 gallons for the second fish + another 12 gallons for the third fish). Most people won’t have a goldfish tank that size.

If you want to keep lots of fish, we recommend choosing a smaller fish than goldfish!

How to calculate tank size?

If you’re reading the above and wondering what size your goldfish tank is, don’t worry – there’s an easy way to work it out.

To calculate your goldfish tank size, you need to take three measurements.

First, measure how long the tank is, from left to right.

Then, measure how wide the tank is, from front to back.

Finally, measure how deep the tank is, from top to bottom.

Once you have those numbers, put them into this fish tank size calculator.

That will give you the number of gallons for your goldfish tank. You can then use the rules above to work out how many adult goldfish you can safely keep.

9 thoughts on “Do goldfish need a big tank? Why goldfish tank size matters”

    • Hi Carolyn – that’s an enormous number of goldfish. When you think that each can grow to several inches long, it becomes clear that there’s no size of tank that you could realistically have inside a home that would comfortably house that many fish. You’d need a large pond for that many goldfish! Sorry if this is bad news for you.

  1. Hi,

    My daughter was given a tiny common goldfish 13 years ago. Obviously I’ve been left with its care. It grown lots & seems healthy but the tank is now a bit small. However I’ve just built a small pond in the garden. There are no other fish in it and the water quality is good and it’s well Oxygenated. We have lots of birds here,no herons that I’ve seen but lots of gulls. there is lots of vegetation cover on the pond.
    Is it a good idea to put a fish that’s only been used to a tank and domesticated for so long in a pond? If so, should I keep feeding it and should I bring it back in winter. Thanks for any advice

    • Hi Richard

      It should be possible to move a goldfish from a tank to a pond. In fact, we have a short article on it here.

      The most important things are to slowly acclimatise your goldfish to the new water conditions and, as you say, to protect them from predators.

      Please do let us know how it goes!

    • Yes they will love it. We have a large horse trough that we put goldfish in. And they do fine even lived when frozen. Lived over 10 years. Also are the bad algae that makes horses sick.

  2. Hi,

    I am pleased that I have found this site as I have a question? I have an oak half barrel water feature with plants and a solar fountain – 38cm H with a 66cm circumference. I was thinking of getting a couple of goldfish so would that work okay?

  3. I won a goldfish at a carnival and they said that I only need a six gallon tank should I get a ten gallon tank I planned to get another one but if I have to get a huge tank I am not sure I can afford it my parents have a pond should I give it to them


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