Betta Fish Tank Size: Which is Best? (How to Choose Correctly)

betta fish tank size
Japanese Fighting Fish is reader-supported. When you purchase through one of our links we may earn an affiliate commission (at no extra cost to you).

Last Updated: July 11, 2022 by Flora Gibbins

Once you’ve seen one tiger barb, you’ve seen them all. Each fish may vary in markings, personality, and health, but the basic form is the same. 


This also applies to most other fish for aquarium keepers. The biggest exception to this rule is betta fish or Siamese fighting fish.

When choosing a betta fish tank size, it is too important to understand how fin shape and physiology impact what tank they can be kept in.


When I first started aquarium keeping, the only betta fish available to consumers were veiltails. These fish have flowing fins and tails that are longer and larger than their body. 

Even though they are exceptionally beautiful fish, they can’t swim very well. 

Today, if you want to buy a betta fish with a smaller tail, you can expect the following:

  • The fish will be more expensive
  • Fewer color and marking options
  • May not be as healthy overall
  • Fin size may still be larger than practical. This makes the betta fish unsuitable for deeper tanks.
If you don’t have a good working knowledge of betta fish physiology and tail shape, it will be tough to figure out which betta fish tank will work best to keep your aquatic pet happy and healthy.

You can easily be misled when looking for an answer to the question, “How big of a tank does a betta fish need?”

betta fish tank size - featured image

The Impact Of Fin Shape, Size, And Structure 

A fish’s tail or caudal fin provides most, if not all, of the power that propels the fish through water. 

You can think of the caudal fin as being like an oar instead of a clipper ship sail. —to work efficiently, an oar has to be in the right shape and stiff. 

By contrast, to be efficient in the air, a clipper ship or sailboat sail can have some give to it.

Since fish live in the water, it is better to have smaller fins with a stiff structure to them. 

Unfortunately, veiltail and other large finned bettas have very little stiffness in their tail and fins. As a result, they can’t swim efficiently in deep water.

Instead of propelling them forward, all that extra weight pulls them towards the bottom of the tank. 

When you row a boat, your arms will eventually become tired. If you don’t exercise much, this will happen very quickly.

The same happens to a betta fish with extra-large fins. Not only does the fish have to compensate for all that extra finnage, it most likely doesn’t have the muscle tone to fight the weight of the water for very long.

Now consider that a betta fish, especially a male, may live in a tiny tub or cramped underwater cell from when it is just a few weeks old. 

Because male bettas are territorial fish, there isn’t enough room to give them all plenty of water to live in as they grow.

There simply isn’t a chance for these fish to develop the necessary muscle tone or gill capacity to live in deeper water.

Therefore, even if the answer to the question “What size tank for betta?” ranges over 1 gallon, you are likely to wind up with a dead fish because the tank is too deep.

Not to mention the fact that many of these bettas come from seriously inbred parent fish. As a result, they are barely healthy enough to live in a tiny tank.

This also results in the answer to the question “How big of a tank do betta fish need?” being lower than some would lead you to believe.

How Swim Bladders Work

Did you know that submarines and fish have something in common? 

When a submarine pilot wants the vessel to go up towards the surface of the water, compressed air is fed into a strategically located, water-filled chamber. 

As the air displaces the water, the submarine becomes more buoyant and heads towards the surface.

While a fish’s swim bladder doesn’t fill with water, it does take air dissolved in the water and use it to make the fish more buoyant. 

Typically, this process is regulated by minerals dissolved or the general hardness of the water. 

Different species of fish require different amounts for their swim bladder to function properly. 

Even though the swim bladder in each species of fish works the same way, body shape determines actual capacity and functionality.

Deep-bodied fish such as fantails have fairly large swim bladders, while angelfish have very narrow ones that tend to constipate. 

Bettas are long-bodied fish, so their swim bladders are on the small side, but not inclined to lock up.

It is important to realize that veiltail and other large finned bettas are nothing like the fish that evolved in nature over millions of years.

You could say a wild fish is a true ideal balance between its internal organs and external fins. As such the swim bladder and fins work together to move the fish easily from one depth level to another.

This is simply not the case with most bettas available for home aquarium keepers.

These fish were selectively bred for extremely large fins. A few generations simply aren’t enough time for the internal organs to catch up with that kind of finnage. 

To add insult to injury, the physics of water weight isn’t accounted for with fins that have little rigid structure.

All of this points to a complete sham when people say it is cruel to keep large finned bettas in small tanks.

These are not the same fish as you find in nature. And they certainly don’t have the internal or external features to live in deeper water.

Some people that answer the question “How many gallons do bettas need?” mention bettas live in rice paddies several feet deep.  

Rest assured a captive-bred veiltail betta put in that setting will drown within a matter of hours.  

Water Weight And Reaching The Surface

A gallon of water weighs about 8 pounds. A betta weighs less than 1/8 of an ounce (2 – 3 grams). 

Now let us say you have an aquarium and fill it with 1 gallon of water. Let’s also say the dimensions of the aquarium kit area confining the water are 8″ x 9″ x 8″, for a total of 576 square inches.

To make the volume math easy, let’s say the depth of the water is 8″. So, the top level of the water weighs 1 pound or .01 pound per square inch.

Now, when you get to the bottom of the tank, you have to add up all the upper levels. So now you are looking at .08 pounds. 

For a betta to go from the bottom of the tank to the top, it must be able to use its swim bladder in conjunction with its fins to overcome that weight. This is something that veiltail and other large finned bettas can do.

Let’s look now at 3 gallons of water with a weight of 24 pounds. Let’s also say the dimensions of the tank are 10″ x 11″ x 15″. So that gives 1650 square inches. 

At the upper level of the tank, you are still looking at around .01 pounds per square inch.

At 8″ down, you are also still looking at .08 pounds.

The problem is by the time you get to 15″ inch depth, the added water weight per cubic inch comes up to .15 pounds.

It may not seem like much to you, but it’s an awful lot on a tiny fish with inefficient fins and an undersized swim bladder.

Even a neon tetra or other small fish will do better than a betta because their fins and swim bladder are adapted for deeper water.

Once you look at the weight to water depth values, it becomes very easy to see why veiltail and other large finned bettas begin to struggle mid-tank in a 3-gallon aquarium; and usually get pulled down to the bottom.

This isn’t to say that a veiltail betta can’t live in 3 gallons of water. It can as long as you keep the depth at 8″ or less, and use a longer or wider tank.

male betta in fish tank

Why Bettas Must Be Able To Reach The Water Surface

Some “experts” claim that bettas don’t actually need to get to the surface to take in air. They claim the ability to take in at least some air is just an evolutionary adaption to oxygen-poor water.

By implication, this means a betta’s gills should be able to supply all the oxygen needs for the fish so long as the water is in good condition.

This is another one of those beliefs that completely ignores basic fish physiology. A fish’s gill efficiency and capacity to resist disease is closely tied to the water type it evolved in. 

As a case in point, tiger barbs evolved in fast-moving water. Their gills simply don’t function as well when they are in slow-moving water.

This video illustrates how fish gills work.  

Bettas are a bit different. Their gills are well designed for slow or still water, even though they work the same way.

Unlike other tropical fish, bettas must have access to at least some air. If they don’t get air, bettas will drown.

Where other fish might not have any specific problem with living at the bottom of a deeper tank, bettas simply can’t do it. 

Once they become exhausted from trying to compensate for oversized fins and undersized swim bladders, they will die.

Fun Fact: Your pet bettas require a thorough knowledge of what they are and who they are friends or enemies with. More important, however, is to learn the distinction between male and female bettas. Read our article, Male vs Female Betta: Key Differences for more information.

Managing Tanks That Are Too Deep

Over the years, I’ve given a lot of thought to putting bettas in 5 gallons or larger tanks. In one sense you can use larger tanks, as long as the water is no more than 8″ deep. 

The problem with this is you are wasting a lot of space unless you make use of different kinds of decorations to fill the area that would have held water.

I don’t recommend using gravel or other heavy objects because excess weight can damage the bottom of the tank and seams.

You can try building a lightweight plexiglass shelf so that water only goes in the upper portion of the tank. 

The other option is to simply fill the lower portion of the tank with water and leave the rest alone.

If you decide to fill only the lower region of the tank, you will still need a hood as part of the aquarium kit. 

Bettas naturally evolved in such a way that they can jump quite a distance and height to find water. 

Even a veiltail betta can easily jump out of a 5-gallon tank.

Fun Fact: If you are into big-sized fish tanks (50 gallons and up), then we suggest you try aerating them more! Larger surface area=more aeration for proper fish survival! Check out the best filter for 100 gallon aquarium (if you have one at home or at the office) to ensure your pet fish’s health and well-being!

Frequently Asked Questions

1. How big of a tank does a betta fish need? 

You can use an aquarium kit of any length and width. 

Bigger tanks (relative to the betta), like a 5 gallon, may be of appeal to you because they will give the fish more room to swim.  Far too many “experts” label 5 gallons as the perfect answer to the question “How big should a betta fish tank be?”

I don’t recommend more than 8″ of water deep for a betta tank size. 

2. How much space does a betta fish need?

As long as the water isn’t too deep, even veiltail bettas will enjoy a larger tank with plenty of swimming room.  

Here is an estimated answer to the question “What size tank for betta?”

 I would say at least 3 – 4 times the body plus the tail length of the fish for a good tank length, and around the same for the width.

Or, you can say a minimum tank size for a betta is around 8” x 9”.  

3. How many gallons does a betta need?

I’ve found veiltail bettas do best in about 1 – 1 ½ gallons of water. The dimensions of the space are more important than the amount of water. 

I don’t recommend going below 1 gallon of water because you must also consider water chemistry. Plants, snail tank mates, and proper filtration need at least this much water to create a functional habitat for a single betta.

4. Would a larger tank expand my betta fish tank mates options?

Not really. Even if the tank is longer and broader, faster-moving fish still need more swimming area than a betta.

Veiltails, in particular, can still get pulled down into oncoming schools of fish and wind up getting hurt in the process.

male betta in tank


The best tank size for your male or female betta has nothing to do with ideas put forth by people that don’t understand the difference between captive-bred bettas and wild ones.

Wild bettas can indeed exist in water several feet deep. However, these fish also have considerably smaller fins.

The sad fact is, millions of captive-bred bettas suffer painful deaths because people put them in tanks that are too big.

About The Author

Leave a Comment

Your email address will not be published. Required fields are marked *