goldfish tank size

What Size Tank Do Goldfish Need?

First-time goldfish owners are always bugged by the question about the correct size of the aquarium or fish tank that they need to put their fish in. We are always presented with the idea that goldfish would do well in a small fish bowl (just watch any animated film or even comic strip and Goldie here is always in a bowl and not in a tank). The point is that any living organism, whether it’s man, cat, dog, or goldfish, will need plenty of space to move about and be happy. The question remains, though. Just how big should the fish tank be to make your goldfish happy? In this goldfish tank size guide we’ll answer this question and a few more to help you become a better pet parent for your goldfish.


Myths Related to Goldfish Living Space Size

One of the most common myths why people put goldfishes into small tanks and fish bowls is that these aquatic creatures don’t live long enough. We’d hate to disappoint you, but goldfishes are known to live up to 30 years. That’s more than twice the average lifespan of dogs and three times that of cats. Did you know that the oldest goldfish ever recorded lived up to 45 years? Goldie from Devon in the UK came from a long line of long-lived goldfishes such as Tish of North Yorkshire that lived up to 43 years.

Impossible! You might say. While the record is unofficial, it just goes to show that proper care of goldfishes can surely make them live a lot longer. And you simply cannot care for them properly if you have an itsy teeny weeny fish bowl to keep them in.

There is another myth, but has some truth to it. Goldfishes tend to grow to their tank’s size. As such, when you put a Goldie into a fish bowl, you really cannot expect it to grow any more than a tiny fraction of the volume of the fish bowl. But, put it in a 60-gallon tank and you could very well be treated to a Goldie that is at least a foot long. The largest goldfish that was ever grown was 15 inches. Weighing more than 4.2 pounds, Goldie was found in Lake Tahoe. We’ve heard of giant catfish and the like; but, a giant goldfish? This one’s definitely for the books.

Putting your goldfish in a tiny space restricts its freedom of movement. It gets super stressed. It doesn’t feel happy. These factors can all lead to its stunted growth. But, if you place the same goldfish in a large fish tank, you are facilitating its growth, development, and happiness.

It is very important to recognize the difference between surviving and thriving. Surviving is, well, merely living without really caring for the conditions upon which the organism is in. Thriving, on the other hand, means growing and continuously developing. For your goldfish, this means getting the right amounts of sunlight, the right temperature and chemical composition of the water, and good nutrition. It also means giving it the chance to explore its environment. You really don’t expect your goldfish to thrive in a fish bowl. Only an appropriately-sized fish tank will.

Tank Size Requirements for Your Goldfish

Because goldfish, like any other living organism, need adequate space to grow and thrive, it is important to get a bigger and longer fish tank. Think of it this way. You feed your fish and it has to eliminate whatever it has eaten somehow. There are no toilets in the fish tank, no commodes or even a pet poop bag for them to put their fishy wastes in.

In other words, they will have to defecate in the same water they are living in. Yes, it sounds yucky and gross. But that just underscores the need for a bigger space so your goldfish will not get sick and die because of the ammonia that is present in their wastes. Sure you can change the water, but you’d have to do it frequently and at regular intervals. You can also put filter into your tank, but you still have to make significant water changes if you want your Goldie to thrive, not just to survive.

So, how big should the fish tank be for a goldfish?

As a rule, the bigger the fish tank is, the better it is for your goldfish.

The current rule of thumb is that the very first goldfish you own should be able to thrive in 30 to 40 gallons of water. We’re talking about single-tail or the common goldfish here. Wow! That’s quite a lot. That’s 30 to 40 gallons for a single fish! But, if you come to think of the size of Lake Tahoe where the largest Goldie was found, a 40-gallon tank is nothing more than a drop of water in the lake. Every time you add a single-tailed goldfish, you will also need to increase the size of the fish tank by another 10 gallons. So if you’re looking to keep 5 common goldfish you’d definitely need a 70-gallon fish tank, at least. You can also use an online goldfish tank size calculator if you don’t like doing the math yourself.

For fancy goldfish – those with really ornate tail fins – the current rule is to put the very first fancy into a 20-gallon fish tank then another 10 gallons for every fish that you put in. If you wish to pet 10 fancies you should have a minimum of 110 gallons for a fish tank.

It is important to remember that common goldfish can grow up to a foot long while fancies are usually smaller at a maximum of 8 inches. Add to this our new-found knowledge that Goldies can live up to 30 or even 40-plus years and you know that a really humongous fish tank is mandatory.

But, if you’re looking to have a pet that will live only about a couple of years and grow to no more than a couple of inches, you’re welcome to put them in a fish bowl. Hopefully, after reading this goldfish tank size guide, you’ll know better.

goldfish aquarium

How Many Goldfish Can Fit in a 10-Gallon Tank?

If you fully understood the preceding section on the size requirements for a goldfish tank, then you know that you cannot fit a goldfish in a 10-gallon fish tank. The smallest possible size of fish tank that you can use is 20 gallons and you can only put a single fancy goldfish. A single common goldfish will require 30 gallons.

You do not want to put a fancy and a common together. Common or single tail goldfish are very fast swimmers and can be real bullies when mixed with fancies. They will swim towards their food a lot faster than their more beautiful counterparts. They can leave fancies hungry. Commons can also nip at the ornate fins of fancies. As such, the final size of your fish tank for goldfish will be determined by the type of fish that you wish to have as a pet.

Going back to our discussion on how many goldfish can fit in a 10-gallon tank, it is clear that the smallest size you can ever get is 20 gallons for a single fancy or 30 gallons for a single common. However, this is not recommended since goldfish are generally known as community fish. They grow and thrive a lot better when in the company of other goldfish like them. It’s similar to dogs that thrive a lot better when in a pack. It’s definitely not like cats, so to speak.

As such, the smallest possible fish tank size you can get for a single tail Goldie is 40 gallons, allowing you to put in a pair of this type of goldfish. For a pair of fancy goldfish, you will need a minimum of 30 gallons.

If you have a 60-gallon tank, then you can put 5 fancy goldfish in there or 4 single tail goldfish. If you have a 100-gallon tank, you can place 9 fancies or 8 commons. You can check with an online goldfish tank size calculator if you want.

Like we said, the bigger the space upon which your goldfish can live, grow, and thrive, the better it is for your aquatic pet. And in case you’re going to have a more difficult time cleaning and maintaining a humongous fish tank, you’d be happy to know that it really isn’t.

You’d be flabbergasted to know that goldfish don’t have stomachs. They only have a very long gut. Food passes down through their gut and exit via their anuses in record time. If you’re lucky, you might even see them eating and defecating at the same time. Gross!

Related Post: Best Goldfish Food

The point is a small fish tank can get really dirty a lot faster than a large tank. It also has greater concentration of nitrogenous wastes. A larger fish tank has a more stable water so you don’t need to clean it very frequently, although you’ll need a really good filtration system.

If you wish to see your goldfish to live 30 to 40 years like Goldie and Tish, then you really have to adhere to the correct size of fish tank. This goldfish tank size guide should help you pick the right size.


  1. How to Take Care of a Goldfish, PetMD

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