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What Tank Size Is Best for Betta Fish? How Small Is Ok?

Something that took me a while to figure out is what size of fish tank I need for my betta fish, but now I know.

Quick Answer

The minimum tank size for a betta fish is 5 gallons, as the betta fish grows roughly 2.5 inches in length, and the rule of thumb is that each inch of fish should have 2 gallons of water. Therefore, a 2.5 inch long fish requires 5 gallons of tank space. However, this is only the minimum.

Keep reading to find out everything there is to know about what size of tank you need for your betta fish, and how small is alright.

What is the Minimum Tank Size for Betta Fish?

As mentioned above, the rule of thumb with most fish is that every inch of fish, which means that every inch in length, should have roughly 2 gallons of tank space. Seeing as a betta fish generally grows to around 2.5 inches in length, one fish should have at least 5 gallons of tank space.

This will help to ensure that the betta fish has enough room to swim around in, to be active, and will also provide you with enough space to outfit the aquarium with a variety of great plants, decorations, and more.

betta fish in tank

However, what you also need to realize here is that the minimum tank size for a betta fish is not the same as the ideal tank size for a betta fish. To answer the main question of the day, 5 gallons for a betta fish is the very smallest you should go.

On that note, you absolutely want to avoid fish bowls, especially ones that are smaller than 5 gallons. Fish bowls are quite simply very inhumane and downright cruel, and no fish, whether betta fish, goldfish, or otherwise, should ever be kept in a bowl.

What Is the Ideal Tank Size for Betta Fish?

As mentioned above, the minimum tank size for a betta fish is not the same thing as the ideal tank size. Although the minimum tank size is 5 gallons, or around 2 gallons for every inch of fish, your betta fish may not be happy with such limited space.

To ensure that your betta fish is happy and has more than enough room to maneuver in, you should give it a full 4 gallons of space for every inch of fish. In other words, if your betta fish grows to 2.5 inches in length, the tank size should be around 10 gallons. Although this might seem like a whole lot of space, remember that betta fish are fairly active swimmers.

They like to swim around, explore different areas, and they even like to hunt as well. Just think of it this way, even though you don’t need more than a few square feet to live technically, it’s always nice to have a little extra space to stretch your legs in.

How Much Space Do Betta Fish Need When Being Kept With Other Fish?

Up until now, everything I’ve talked about has been about keeping a single betta fish alone, which is perfectly fine. Remember that betta fish are extremely territorial and aggressive fish, which means that keeping them together with others is going to be a problem.

This is especially the case that we are talking about keeping betta fish along with other betta fish. On that note, if you want to keep multiple betta fish together, you’ll have to keep either a male and a female, or several females together, although these situations can also cause problems.

In the grand scheme of things, keeping various betta fish together in the same aquarium is not recommended, because they will inevitably end up bullying and harassing each other, due to territorial issues. 

However, there are other tank mates that may be suitable for betta fish, especially ones that don’t look like betta fish. As long as the betta fish does not mistake any other fish for a betta fish, they should remain relatively peaceful.

With that being said, to help keep the peace, you want to give the betta fish plenty of space inside of a fish tank when being kept with other fish. Although above we talked about giving a single 2.5 inch long betta fish a 10 gallon tank, if you plan on keeping it in a community setting along with other fish, you might want to increase that yet again.

If this is the case, you may want to provide each inch of your betta fish with at least 5 gallons of water. The result here would be that a betta fish should have at least 12.5 gallons of water to itself in an aquarium, not counting the space used by other fish.

What Happens If Betta Fish Don’t Have Enough Space?

For argument’s sake, let’s just take a quick look at what might happen if the fish tank you choose for your betta fish is not large enough.

Territorial Issues

Although this may only be an issue if your betta fish is being kept in a group along with other fish, if the tank is not large enough, there will be territorial disputes and aggression issues.

The simple reality is that betta fish are some of the most aggressive tropical fish that you could keep in a home setting, and they need their space.

They will most definitely get into fights with other fish if they feel as though their territory is being encroached upon. This is the case whether the betta is being kept with other betta fish or other species.

Bioload and Water Quality

Something else to consider here is that the smaller the tank is, the faster the water gets dirty. It’s not like betta fish are overly dirty fish and they don’t produce a huge bioload, but it still adds up over time.

A betta fish leaves some food uneaten in the water, plant matter deteriorates, and fish waste itself releases a variety of organic poisons into the water, with ammonia being one of them.

The smaller the tank is, the dirtier the water gets, and the bigger the chance of your fish becoming stressed out and suffering from issues due to poor water quality.

More Frequent Cleaning Needed

What it really comes down to if your fish tank for your betta fish is too small is that you’ll have to clean it much more frequently, plus your filter needs to be up to the task as well.

Your filter needs to be able to process at least two to three times the amount of water in the tank every single hour, and the smaller the tank is in comparison to the fish, the harder the filter has to work to keep the water clean. 

Therefore, your best bet is to simply get a larger tank, because it’s much easier to maintain in this sense.

A Big Betta Fish Tank Setup Tip

In terms of the spatial requirements for your betta fish, a great idea is to put a lot of plants and decorations in the tank. Now, we aren’t talking about stuffing a bunch of plants into a very small tank, but rather choosing a large tank and then filling it with nice decorations.

This is especially a good idea if you plan on keeping your betta fish along with other fish. All of those decorations and hiding spots will provide the betta fish and the other fish with some peace and quiet. At the very least, it will make a betta fish feel like the territory still belongs to it, even though there are other fish present.


At the end of the day, betta fish require a good deal of room, especially if you plan on keeping them with other fish. However, at the very least, your betta fish should have 5 gallons of tank space, with the ideal tank size for any 2.5 inch long betta fish being around 10 gallons. Remember, in this case, bigger is better.

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