Goldfish Tank Size 101: Do they need a big tank to grow?

Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: April 8, 2024
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We’ve all seen the typical set-up for a goldfish at pet stores – typically composed of a single fish, a small aquarium, potentially a few elementary live plants, and a bubble maker for decoration. But does this aquarium’s size really meet the requirements of an average goldfish? Can they truly flourish and lead their happiest, most fulfilling lives in such a confined space?

If you’ve ever wondered any of these questions about what the right size of goldfish tank is for your freshwater fish, read on through this goldfish tank size guide for the answer to these and more!

Article Summary

  • Goldfish size is influenced by factors like their type, tank conditions, and diet, with average sizes ranging from 2-5 inches for single-tailed goldfish and up to 12 inches for comet tailed goldfish.
  • A good rule of thumb is to start with a minimum tank size of 20 gallons for 1-2 goldfish, adding 10 gallons per additional goldfish.
  • Opting for a larger tank can provide more stable water conditions, allow for more fish to be kept, give the fish more swimming space, be easier to maintain proper filtration, and offer more room for decorations and plants.

How Important Is Tank Size For Goldfish?

Goldfish in a Planted Tank
Goldfish in a Planted Tank

Tank size plays a huge role in the overall health of the common goldfish. They need an adequate amount of room in which to swim, as well as proper water flow to provide an oxygenated environment, remove harmful wastes and keep the tank clean.

In the fish keeping world, planning a fish tank for the long term, including how many goldfish you intend to keep, is key in creating a healthy environment.


To give an idea of just how long-term you may want to be thinking, the world record for oldest goldfish is held by Tish of the UK. This remarkable fish made it to 43 years of age and lived in a small fish tank!

Without the right size goldfish aquarium, you will likely see a lethargic, sick fish that deteriorates over time from as little as a day to a few weeks.

Lack of swimming space and improper filtration can quickly add up into a dangerous situation for your goldfish and other fish in the aquarium, leading to fatalities. For example, in a small fish tank with many inhabitants, if one of your fish contracts Ich, it can quickly spread to the other fish.

Can Goldfish Live In A Bowl?

We’ve all seen the plethora of goldfish bowls on sale at our local pet stores.

We’ve also heard horror stories about fish bowls being torture for some fish, with our precious pet fish gasping without enough oxygen and looking depressed with not enough space to swim.

So what’s the real answer to this question?

Depends on Tank Conditions

In short, if conditions within the bowl are adequate for what goldfish require, then a goldfish bowl can work just fine.

Keeping goldfish in a bowl is not animal cruelty by any means, but if there is poor water quality, harmful chemicals, inadequate surface area for gas exchange, and little water movement, the goldfish will not be able to live a healthy life.

Not Just About Tank Size

Even a large tank can be a poor choice compared to a smaller fish bowl with better filtration and water quality.

Swimming space and surface is important, but if your aquarium fish can’t breathe due to a lack of dissolved oxygen, things will not work out well.

Goldfish Bowl Without a Filter

Goldfish in a Bowl
Goldfish in a Bowl

Keeping a goldfish in a bowl without a filter will not work.

The water quality will drop rapidly as the fish waste piles up, and you’ll see your pet fish deteriorate and suffer as a result.

Using an air pump can be a great way to introduce water movement into the aquarium, but it needs to be coupled with proper filter media.

How Big Can Goldfish Grow?

The size to which your goldfish will grow is influenced by several factors, such as the goldfish type, the conditions of the tank it lives in, and the type of diet it receives.

The average single tailed goldfish will grow to around 2-5 inches in size throughout their lives. Baby size goldfish can grow 1-2 inches in the first year or so of life.

Upon reaching adulthood after around a year this is followed by ½ to 1 inch per year after that. With this in mind, it’s important to know that as your fish grows, you may need to look into a bigger tank to support it.


The world record length for a goldfish is held by a Norwegian fish who grew to an astounding 18.7 inches long throughout its life, now that’s a large fish!

Comet Goldfish Growth

The comet tailed goldfish can grow to a slightly larger size over time, around 4-12 inches. Therefore when considering comet goldfish tank size you may want to aim a little higher or at a larger aquarium, at 25 gallons for your first fish and 10 gallons additional space per fish after that.

Goldfish Tank Size Myth

There is a popular myth out there that a goldfish will continue growing to fit whatever size of fish tank it is placed in.

While this isn’t necessarily true, there is a small kernel of truth to it.

Here’s a quick informative video about goldfish growth.

How big do goldfish get

In general, fish kept in a smaller aquarium will tend to stay smaller. They may not have adequate swimming room, leading to a less active fish which produces its own growth inhibiting hormones.


Big tanks mean more room for your fish to swim, and this paired with a good diet and continuous water quality maintenance will see your fish grow to its maximum potential size.

What Size Tank For Goldfish?

Goldfish Under Blue Light
Goldfish Under Blue Light

Are you looking at having more than a single fancy goldfish in your fish tank? You’ll need to size up accordingly since they have delicate fins.

Looking to focus on just one single tail goldfish? You can probably get away with a small space, or even a nano tank for your little fish!


Many stores sell premade kits for goldfish tank builds, but be aware that these may not always meet the minimum healthy size requirements for your fish. Be sure to do your homework before jumping on board something just because it looks simple or easy!

Tank Size Rule of Thumb

A good rule of thumb for goldfish is to start with a minimum tank size of 20 gallons (or around 3 foot long) for 1-2 fish, with an additional 10 gallon tank size per goldfish living in the tank after that. This means that for a tank with 4 goldfish, you’ll need a minimum of 40 gallons, and so on beyond that.

What Is A Good Size Tank For A Goldfish?

While a ten gallon fish tank or small bowl is going to be too small, anything over 20 gallons should provide enough room for one fish.

When looking at many goldfish or additional goldfish tank neighbors, especially if you don’t know their gender, you’ll want to consider tall tanks or larger ones with increased water volume and more swimming space. This will not only keep your goldfish happy, it will keep them healthier in the long run.

Waste And Goldfish

Goldfish produce more waste than most other species.

Because of this, whether keeping common goldfish, Shubunkin goldfish, Ping Pong goldfish, or Bubble-eye goldfish, you’ll want to look at an appropriately sized tank and adequate filtration system.

Waste Buildup

The problems with waste really start to add up when keeping goldfish in a small tank or nano tanks, as the slim bodied fish produces enough waste to overwhelm the lack of water movement.

Frequent water changes of 10% per week or 20-25% every two weeks, along with ensuring adequate water movement and filtration are key in keeping your goldfish healthy in the long term.

Do Goldfish Need a Big Tank?

Goldfish Swimming
Goldfish Swimming

One goldfish can be just fine with a small fish tank of 20 gallons or so.

When considering additional fish, you’ll need to either look at getting a larger tank with more space, or moving to several small tanks where your fish can live separately.

What Size Tank Do Goldfish Need?

Considering that goldfish are a social fish, you may want to plan on having other goldfish in the same tank.

You’ll want to look at how many goldfish you’re intending on keeping overall, and plan accordingly. Even if you only want two goldfish, you should get the largest possible tank you can afford.

Adult Goldfish

For more than one goldfish (full grown adult), you should consider an additional 10 gallons of size for your fish tank.

This means that for 4 goldfish, you would want a minimum tank size of 20 gallons for the first and 10 per each after that, for a total of 40 gallons of water for all four.

Why Consider Having a Bigger Tank?

While this may seem like it adds up quickly, goldfish keeping is all about creating established tanks that provide the most enriching environment for your fish’s long term health.

Going with small tanks because they are cheaper and easier to maintain is, quite simply, inadequate care and will lead to sick or lethargic fish.

What Does My Goldfish’s Tank Need?

Along with the adequate space, goldfish prefer a few different things with regards to the perfect set up.

It’s important to consider the overall setup for your fish, including tank position and surrounding atmosphere when creating the best place your goldfish can live their life.


In terms of equipment, you’ll also want to consider a filter and aeration of some kind (air stones, air pump, etc), a separate tank and appropriately sized net for tank cleaning.

Having everything on hand before you need it makes a huge difference when it comes time to clean or move your fish.

Tank Lighting and You

While goldfish are daytime creatures, also referred to as diurnal, they do still need to have a regular, consistent day night cycle. Make sure that your goldfish have around 8-10 hours of darkness each day so that they get the healthy amount of sleep that they need.

Having a hard time remembering when to turn off the lights in your tank? Consider using an aquarium timer in your tank!

While the darkness doesn’t need to coincide with the actual day night cycle of their natural habitat, it does need to be consistent!

What About Live or Plastic Plants?

Planted Aquarium
Planted Aquarium

Plants can be a great choice for a goldfish bowl! Not only will your fishy friend enjoy the occasional nibble, but it will love having the break in eye line and something to swim around.

Goldfish owners have numerous options when it comes to goldfish plants, but for those who are just starting out, a simple and easy plant to begin with is java moss.

These live plants are found in most pet shops and have a simple care regimen.


Additionally, plastic or fake plants can be a good option for those who’d rather skip the plant food care and go with something artificial. These do still need to be cleaned consistently, as bacteria can grow on them.

Tank Temperatures for Goldfish

Goldfish are generally considered a cold water fish, and prefer a water temperature between 50 and 60 degrees Fahrenheit.

They are fairly capable of tolerating changes around 10 degrees above or below this norm, but swinging too rapidly or too high/low can lead to temperature shock for your fish.


If you know that your fish tank is in a location that will be more exposed to the elements, such as for certain freshwater pond fish, you may want to consider using a water heater in your goldfish tank or pond.

Filtration in a Goldfish Tank

Proper filtration is critical when setting up a tank for goldfish! They produce a lot of waste in your freshwater, and in a small tank this can add up quickly and can overwhelm your filtration system.

Air Stones

An air stone or bubbler may be needed to get things moving so that the filter can actually remove the waste, but keep an eye on the filter itself and clean it regularly along with regular water changes.

The good bacteria in your tank play a major role in helping the fish in the cycle of nitrogen. These bacteria work to fix nitrogen into nitrates and nitrites, which are further reduced by other bacteria that grow on the substrate within your tank.


Throughout today’s article, we’ve looked at the proper size for goldfish tanks, some goldfish care tips, as well as some considerations regarding having more than one fancy goldfish in a single fish tank.

The best rule of thumb is to start with a minimum of a 20-30 gallon tank for a single common goldfish, with an additional 10 gallons of water per fish after that.

Thanks for reading! I hope that this article was helpful.

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