Do goldfish need a big tank?

Yes! Goldfish do need a big tank. It’s cruel to keep goldfish in a bowl, so giving your goldfish enough space is one of the most important parts of proper goldfish care.

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.

You might be surprised to learn just how big goldfish grow.

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

Some goldfish have grown even bigger.

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 size tank does a goldfish need?

Common and Comet goldfish tank size

For Common goldfish and Comet goldfish 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, we recommend:

  • 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!

How to calculate tank size?

To calculate the size of your goldfish tank, 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.

4 thoughts on “Do goldfish need a big tank?”

    • 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!


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