Betta Fish Tank Size: How Big Should My Betta Fish Tank Be?

The perfect betta fish tank size depends on many different factors. However, at its most basic, a 5 gallon tank should be considered the bare minimum for a single fish. That said, a larger tank is almost always better if you can afford it.

Misunderstandings About Betta Fish Tank Sizes

There are many misunderstandings and urban myths surrounding tank sizes for betta fish.

These come from a number of sources:

Aquarium Shops: Most of the betta fish we see are in aquarium shops, where they are kept in tiny little containers. This is primarily so that the store can display a wide number of specimens without them coming into contact with one another – and therefore fighting.

It is important to realize that this is really only a temporary solution, and that betta fish kept in these conditions are likely to have a much shorter lifespan than when kept “properly”.

Natural History: Many aquarium hobbyists know that betta fish are found naturally in rice paddies and swamps in Southeast Asia. Furthermore, there are many forum threads which discuss how these bodies of water can dry up when rainfall is low.

This leads many keepers to assume that betta fish can survive in just a few inches of water. While this may be theoretically true, it is important to highlight that they’re merely surviving – rather than thriving.

Hobbyists: Betta fish can be surprisingly shy and retiring creatures. In the wild they encounter many different plants, fallen branches and more, which create plenty of hiding places.

All too often in the fish keeping hobby a betta fish is placed into a bare tank, devoid of any tank decor, where upon your betta fish may cower in one corner, barely moving around the aquarium.

This has led some hobbyists to suggest that betta fish don’t like large tanks, though this is a long way from the reality.

Fortunately we’re going to put all these misunderstandings to bed, and explain what the ideal tank size is for a betta fish.

Factors That Influence Betta Fish Tank Sizes

In order to choose the “perfect” betta fish tank, there are a number of factors that should be considered:

Water Chemistry

One of the most important elements relates to the water chemistry in your betta tank. If you’ve kept fish before then you’ll know that the waste products produced by your fish, together with any uneaten fish food, can be toxic to your fish.

In a properly acclimatized tank these chemicals should slowly be broken down into less harmful versions, which are kept under control with regular partial water changes.

The thing to bare in mind is that the smaller your tank, the less water it contains, and therefore the sooner these levels of ammonia, nitrites and nitrates will reach dangerous levels. Think of the difference between pouring a cup of dye into a bath versus a swimming pool.

While some experienced fish keepers do use very small betta fish tanks, they require almost constant attention to maintain the correct water chemistry. For the rest of us, a larger tank cuts down on our workload and helps to keep your betta fish in top condition.


We’ve already discussed the importance of water quality on the health of your fish. One key ingredient here is installing a suitable filter. Over time, a colony of helpful bacteria will begin growing in your filtration medium, and they in turn will improve your water chemistry.

This means that unless you want to carry out daily water changes on your betta fish, a reliable filter should be considered essential. Fitting a filter can be problematic in smaller aquariums, but a larger tank size gives you far more options.

Another factor to consider here is that betta fish naturally come from slow moving waters.

Their brilliant fins and frills can make it difficult to swim in fast-moving water. In a small tank the filter output is far more likely to create uncomfortable currents, while in larger tanks this is far easier to avoid.


Coming from tropical areas such as Thailand and Burma, your betta fish will require warm water if it is to thrive.

Even if you’re lucky enough to live in a very warm area – such as the southern United States – temperatures can still fluctuate significantly over a 24 hour period. An aquarium heater therefore helps to maintain a constant, reliable temperature for your fish.

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This affects the size of your betta fish tank in two ways. Firstly, you’ll need to ensure that any tank you choose is large enough to fit an aquarium heater inside. With particularly small tanks this can be surprisingly challenging.

The second element to consider is that larger bodies of water heat up and cool down more slowly than smaller volumes.

This means that a larger tank will stay warm for longer if you’re unlucky enough to suffer a power cut. It also means that your fish will have longer to acclimatize if you experience a sudden summer heatwave.  

Aquarium Shape

Like all fish, bettas breathe oxygen that they extract from the water using their gills. While betta fish can breathe air in some circumstances, it is important to ensure enough oxygen is available in the water.

There are a number of ways to achieve the right oxygen levels, but one of the most common is to position the outlet of your filter so that it creates gentle ripples on the surface of the water. This, in turn, allows oxygen to permeate into the aquarium water.

The crucial point here is that the larger the surface area of the water, the more easily oxygen is absorbed. This is why so many aquariums are long, rather than tall.

Generally speaking, when selecting a betta fish tank, it is best to find a tank that has as large a surface area as possible, which generally means that larger tanks are best.

Tank Mates

There is a reason why betta fish are sometimes referred to as “Siamese Fighting Fish”. The males, in particular, can be tremendously territorial. Keeping two of these fish in the same tank can lead to fighting, and even the death of one or both fish. As a result, many people assume that bettas must be kept alone, but this is isn’t exactly true.

While you shouldn’t keep a male betta fish with another of its kind, there are a number of other animals that can be included in your tank. For example, some betta fish keepers opt to include snails, shrimps, and even some smaller and gentler fish.

Click here if you want learn more about suitable betta fish tank mates.

Once again, however, this can affect tank size. If you’d like to keep your betta fish in a community setup then a larger tank will be required, so that each inhabitant can have it’s own space.

Do Betta Fish Get Lonely?

While there’s no denying the beauty of a lone betta fish, some keepers do worry whether their betta fish will get lonely. Unlike some other popular pet fish, bettas don’t swim in shoals and can be so territorial that they actively chase off other fish. They’re not exactly the social butterflies of the fish world.

In an aquarium the luxurious fins of the betta fish can also cause issues. Some other fish – such as Tiger Barbs – may try to nip at these fins. The end result can be a scruffy looking betta fish, or one that spends its life in a constant state of stress thanks to the bullying.

The end result is that betta fish don’t get lonely. While they can be kept with a range of other invertebrates or fish, the decision to do so is more about what you find attractive and interesting, rather than anything else. If in doubt, keeping your betta fish alone will prevent any chance of fin nipping or fighting – both of which can help your fish to stay happy and healthy.

What Size Tank is Best for a Betta Fish?

In brief, betta fish should be kept in a tank so smaller than 5 gallons – and I would personally advise you to use a tank of 10 gallons or more if you can afford it.

Do Betta Fish Like Big or Small Tanks?

One of the more common questions to be asked is whether betta fish prefer big or small tanks. As with so many other things, the answer is “it depends”.

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Firstly, small tanks have a number of problem associated with them, such as difficulties in maintaining water chemistry and temperature.

Big tanks, on the other hand, can be quite plain and clinical, and your betta fish may spend its time trying to hide in one corner.

To answer the question I would argue that betta fish themselves have no specific preference on tank size. At the same time it is much easier to give your betta fish the conditions it needs in a larger tank.

So long as you’re intelligently using tank decor to provide areas where your fish can hide then a larger tank is better than a smaller tank for bettas.

Can a Tank Be Too Big for a Betta?

The natural environment of the betta fish can be filled with interest. Rocks, branches, plants and more all add an extra dimension, and allow the freshwater life that survives there to keep their distance from one another.

A bare, decor-less aquarium is quite a different environment, and fish can get stressed without the ability to hide away from view.

As we’ve seen so far in this guide, generally speaking a larger tank is better than a smaller one for a whole host of different reasons. The only way that a tank can be “too big” for a betta fish is if it hasn’t been set up properly with places to hide.

Add enough interest with aquarium plants, rocks, caves and so on and your pet should be overjoyed at the swimming space available.  

What To Look for in a Betta Fish Tank

Now you understand all about betta fish tank sizes it makes sense to discuss some of the most important factors to consider when actually choosing your first betta fish tank…

Large Surface Area

A tank that is long and wide, rather than tall and narrow, allows more oxygen to enter the aquarium water. This, in turn, ensures that your fish has plenty of oxygen to breathe. Note that the warmer the water, the less oxygen it holds, so this is particularly important for tropical fish.

Close Fitting Lid

While betta fish may seem to move slowly and elegantly around their tank, you might be surprised to hear that they can be very good jumpers.

The last thing you want is to find your betta fish dead on the floor after they leapt from their tank. A close fitting lid helps to prevent this happening, and also limits the evaporation of water from the tank.

Room for Electricals

At a bare minimum you’re going to need a filter and an aquarium heater. Both of these take up room in an aquarium.

When choosing a betta fish tank, therefore, don’t make any final decisions until you’ve also selected your filter and heater. Ensure that they easily fit inside the tank, and still leave a generous amount of swimming space for your betta.

Built in Equipment

Smaller aquariums suitable for betta fish increasingly come with their electrical equipment built in. Of course, this can be very handy, as it not only saves money but also ensures that everything is built to work together.

While they may initially seem pricey, therefore, these “all in one” tank kits are actually well worth a look.

Richard Adams

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