Goldfish Tank Size: A Beginner’s Guide To Aquarium Setup

goldfish tank size
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Last Updated: July 8, 2023 by Flora Gibbins

The ideal goldfish tank size has raised numerous debates across fish forums. Some fish owners argue that goldfish are comfortable in fish bowls, while others recommend getting larger tanks.

Well, actually…

Goldfish prefer larger tanks with adequate room for swimming. Whether you own a common goldfish or slim-bodied fish, these fish will thank you for the extra space in a larger tank.

This article explains the best tank size for goldfish and what to include in a goldfish tank. Keep reading.

Ideal Tank Size For Goldfish

You should first understand how big your goldfish will grow to calculate the ideal size of a goldfish’s tank. That small goldfish you brought home from the pet store can easily grow to reach between 10 to 16 inches long.

goldfish in aquarium with green plants

To keep the goldfish in an ideal tank, here is a simple breakdown of the size of each full-grown adult goldfish.

Type Of Goldfish Goldfish Length
Fancy Goldfish 8 inches
Single Tail Goldfish 12 to 16 inches
Common Goldfish 10 to 12 inches
Comet Goldfish 10 to 16 inches
Shubunkin Goldfish 10 to 12 inches

The minimum tank size for one fancy goldfish is 20 gallons, and 30 gallons for one common goldfish.

But bigger is always better.

Fancies swim clumsily and do not need a deep tank. Instead, a 20-gallon tank measuring 3 feet long will be perfect for one fish. If you want to add more fancies, provide an additional 10 gallons for every fish. This means 30 gallons for two fish, 40 gallons for three fish, and so on.

On the other hand, comets and common goldfish should be kept in a 30-gallon tank. These goldfish grow over 15 inches long. So, when housing two common goldfish, provide 12 more gallons for every additional fish. This means that two fish need 42 gallons of water.

Getting a bigger tank ensures your goldfish have adequate swimming room plus water volume. These very active fish need sufficient room to move around and reach their maximum length.

When calculating the best goldfish tank size, consider the space you need for other tank mates, decorations, and tank equipment. These decorations and equipment should not take up the fish’s movement space.

6 Reasons Why You Should Get A Big Tank Size For Goldfish

Goldfish bowls and smaller tanks inhibit a goldfish’s growth and overall lifespan. To avoid this, we recommend keeping goldfish in their ideal tank size due to the following.

1. Full-Grown Goldfish Have Large Bodies

When buying baby goldfish at the store, they may be 2 to 4 inches. With time, these fish grow to reach 12 to 16 inches long.

goldfish in an aquarium

Goldfish require enough room to swim and move their long bodies at this length.

2. Goldfish Need Room To Swim

Did you know fancy goldfish are not as agile as other fish? This is due to their long fins, compact body shapes, poor vision, and heavy head growth. Fancy goldfish need a bigger aquarium that will enable them to turn easily when maneuvering.

On the other hand, common goldfish are agile. They charge super fast and are incredibly energetic. But, their wide, bulky bodies compromise their turning ability. Like fancy goldfish, common goldfish need a large tank with more room to swim.

3. Bigger Tanks Mean More Oxygen Levels

goldfish in aquarium with zen stone and bubbles

The larger the surface area, the better the water aeration. A bigger tank with a larger surface area will promote gaseous exchange. Oxygen will easily enter the water as carbon dioxide leaves.

4. They Are Social Fish

Unknown to many, goldfish are social shoalers who prefer the company of other goldfish. If you keep two goldfish together, you may observe them swimming close together, sitting, or sleeping together.

various goldfish in aquarium

Keeping goldfish with other goldfish provides them with social interaction and security.

You should provide at least 40 gallons for three fancy goldfish considering the minimum tank size for a single fish is a 20-gallon tank.

Add a few more gallons to provide more shoving room during feeding time. These fish compete over food. Providing a small tank can lead to aggression, irritability, stress, and diseases.

5. Goldfish Produce A High Bioload

Moreover, goldfish require a big tank because they produce a high bioload. These cold-water fish are messy eaters with large appetites. They produce high ammonia levels that can prove toxic for the fish.

Here is a YouTube video on lowering ammonia levels in a goldfish tank:

6. Goldfish Live Long

Most goldfish live for 10 to 15 years, with others reaching 20 years. This is a long time for a fish to spend in a nano tank. Small tanks do not have adequate swimming space or room for décor.

This is why we recommend housing your goldfish in a bigger tank to keep your fish happy throughout their life. The tank will keep goldfish entertained, encourage socialization, and provide more swimming space.

Fun Fact: You have two options: (a) jump in to read a related article of ours or (b) continue reading this post until the end. Either way, you get to have excellent coverage of how big goldfish tanks could get and what requirements they need to care for your aqua buddy. You can read our related story post here — Goldfish Tank Setup: A Beginner’s Guide In Assembling One.

 4 Aspects To Include In A Goldfish Tank

An ideal goldfish tank requires filtration, enrichment, and enough swimming space.


As previously mentioned, goldfish produce a high bioload which can easily build up in nano tanks. So, you need to install a powerful filtration to keep the goldfish tank clean.

When choosing a filtration system, get one whose flow rate is 10 times the tank’s volume.

For instance, a filter with a flow rate of 200 gallons per hour is perfect for 20-gallon tank size.


goldfish in fish tank with decorations and bubbles

Goldfish are intelligent fish species that need an enriched environment to lead a healthy life. You can provide this by adding live plants, bogwood, rocks, floating balls, mirrors, and other decorations.

Also, include an air pump to promote aeration, particularly for goldfish with heavy head growth.

Swimming Space

Goldfish spend their day moving around the tank. These fish do better in long tanks since they move horizontally, not vertically. Therefore, goldfish tanks should feature plenty of long swimming room to facilitate their movement.

Moreover, these fish need places to explore and hide. Therefore, include plenty of plants and decorations. Avoid a tiny bowl since it will neither provide room for swimming nor decorations.

Water Quality

Poor water quality can negatively impact your goldfish’s health. This is why you should make regular water changes to prevent ammonia and nitrate buildup in the goldfish tank.

goldfish with green plants and stones

The ideal weekly water change for established tanks is 20 to 25%. You will have to perform more frequent water changes in a small tank.

Additionally, clean the filters every two weeks and replace the filter media after a few months. Also, vacuum the gravel once a month to maintain water quality.

Related Questions

Do Goldfish Outgrow Smaller Aquariums?

It depends on how you maintain the goldfish’s environment. Goldfish produce a potent growth-inhibiting hormone (GIH) that suppresses growth. When this hormone is concentrated in the goldfish aquarium, it stunts the fish’s growth.

Performing regular water change dilutes the growth-inhibiting hormone.

This means goldfish in smaller tanks will have limited growth than fish in larger tanks. But, they can outgrow the smaller aquarium if you perform regular water changes to prevent the concentration of the GIH hormone.

How Many Goldfish Can I Keep In A Goldfish Aquarium?

The answer solely relies on your preference. These freshwater fish need enough room for swimming, enrichment, proper filtration, and a clean, healthy environment to thrive. Avoid overstocking as it can result in stress and premature death.

Can I Keep Goldfish In A Goldfish Bowl?

We do not recommend fish bowls or small aquariums for goldfish keeping. Smaller tanks are more prone to poor water quality, ammonia and nitrite poisoning, and aggressive behavior among goldfish.

Goldfish can survive in a bowl, but they will never truly thrive. Therefore, provide a 20-gallon size tank as the minimum tank for one goldfish and ten more gallons for every additional fish.

Why Do Local Pet Stores Recommend Small Tanks For Goldfish?

Some stores are primarily set up for business and profits, while others do not have detailed information about the best goldfish tank size. Small goldfish tanks can only house juvenile goldfish for a few weeks before they outgrow them or have stunted growth.


Goldfish are hardy fish with a long lifespan when kept in the right tank size and water conditions.

A 20-gallon aquarium should be the minimum tank size for one fancy goldfish and a 30-gallon tank for common goldfish. Nevertheless, these large fish will be happier in larger tanks.

Always keep the goldfish tank clean through filtration and perform regular water changes. The aquarium should also provide enrichment to these intelligent fish.

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