What Size Fish Tank Should I Get?

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A lot of novice aquarists overlook the importance of getting a fish tank that is the correct size.

If you end up getting a fish tank that is too small it can cause lots of problems, think: stunted growth, aggressive fish, and unstable water parameters.

Each one of these issues can ultimately lead to your fish dying.

So, in this article, we are going to look at what size fish tank you should get before answering whether bigger aquariums are “better”.

What Size Fish Tank Should I Get?

Lots of people get into fishkeeping by first purchasing an aquarium, and then wondering which fish they should get.

This is the wrong way to approach it.

Chances are, you want to start keeping fish because there is a particular breed of fish that you want to keep.

So my advice to you would be to start with the fish.

Sit down and think about the type of fish you want to keep and also how many fish you intend to keep. Once you’ve figured this out, you can work backward and figure out exactly how big your fish tank should be and also which type of fish tank you should buy (more on that later).

The only time I wouldn’t recommend this is if you’re on a very tight budget.

If you’re on a tight budget and don’t have much spare cash, I would recommend waiting until you can afford to buy and keep the fish that you’d like.

However, if you simply can’t wait, I’d recommend buying the aquarium first and then figuring out how much money you have left to buy your fish with.

Large Public Aquarium
Large public aquarium

Bigger Aquariums are ‘Better’?

As eluded to earlier on, generally speaking, the bigger the aquarium the happier your fish will be.

Why is this the case though?

Well as we mentioned earlier on: in small, cramped, environments fish become stressed and aggressive. The opposite happens when fish have lots of space.

Second, larger tanks are far easier to maintain.

As most aquarists will attest to, the biggest problem we generally face is maintaining the water conditions inside the tank; mainly water chemistry and temperature.

Now, the larger the aquarium, the more stable the water is, and crucially, the easier it is to keep stable.

It takes longer for ammonia to spike in larger tanks so you have more time to react if something goes wrong. As a result, a 100-gallon tank is far easier to keep stable than a 30-gallon tank. And again a 30-gallon tank is far easier to keep stable than a nano tank.

This means that the water conditions in a larger tank are more likely to be within healthy tolerances which results in happier fish!

Popular Fish and Their Tank Size Requirements

SpeciesMinimum Recommend Tank Size (Individuals)Minimum Recommend Tank Size (School)
Green Chromis10 Gallons40 Gallons
Common Clownfish10 Gallons60 Gallons
Royal Gramma30 Gallons100 Gallons
Oscar60 Gallons150 Gallons
Neon Tetra5 Gallons15 Gallons
Guppies5 Gallons20 Gallons

Avoid This Mistake

Small Aquarium
Avoid Small Aquariums

One of the biggest beginner mistakes I see is beginners buying a “starter” tank.

When new aquarists first start, they tend to buy a very small tank, regardless of the species of fish they want.

Although this means that the hobby is affordable and makes it accessible to more people, this is not the ideal way to start. Unfortunately what often happens is people get a small fish tank, such as a 25-gallon tank, and then purchase fish that need more space.

A common example of this is with Oscars.

When the oscar fish grow from a juvenile to an adult and needs more space, you can buy a bigger tank for them. In my experience, this rarely happens.

People see their Oscar fish surviving in a small tank and think they must be fine, in reality, the confinement is hurting them and reducing their life span.

You should always buy the right sized tank from the start. Figure out how much space your fish need (as an adult) and place them in a suitably sized aquarium from the get-go.

If you put fish in a small aquarium it can cause lots of problems.

Common Problems with Small Aquariums

There aren’t many problems that occur when you have an aquarium that is too big. In fact, as a general rule it’s often said: the bigger the aquarium the happier your fish will be.

However, when you have an aquarium that is too small, it can be devastating for the fish in the tank.

Placing fish in a tank that is too small can cause countless problems, here are the biggest 3 problems it causes:

Nano Coral Reef Aquarium
Nano coral reef aquarium

Issue 1: Stunted Growth

There is a common myth amongst beginner aquarists that:

“Fish only grow to the size of the tank”.

Before I progress let me say here that this is entirely false.

This myth has come from people who keep goldfish. Goldfish are indeterminate growers which means they continue to grow until they die. As you may already know, when placed in a small aquarium goldfish won’t continue to grow. People wrongly assume from this that fish simply grow to the size of the tank. Wrong.

What actually happens is the fish’s growth is stunted and their health has been permanently damaged as a result.

Issue 2: Reduced Lifespan

Not only will placing fish in an undersized aquarium stunt their growth it will also significantly reduce their lifespan.

According to scientific research, it reduces their lifespan because of two key reasons:

  1. Firstly, in small spaces fish become stressed. This stress places an excessive amount of tension on their heart and causes it to overwork.
  2. Secondly, it causes internal organ failure. As mentioned above, placing fish in a tank that is too small causes stunted growth. This means that the fish’s internal organs don’t have enough space to grow. Ultimately it ends with internal organ failure.
Small Home Aquarium
Small home aquarium

Issues 3: Enhanced Aggression

Finally, the other big problem it can cause is behavioral issues.

There are numerous behavioral implications such as stress, fear, and anxiety. But perhaps the biggest issue it can cause is enhanced aggression.

Fish kept in small enclosures can turn aggressive towards the other fish in the tank; this is because they are stressed and scared.

Unfortunately once a fish turns aggressive it is incredibly difficult to turn them back into a friendly communal fish.

The easiest way is to not allow them to become aggressive in the first place!

What’s the Best Sized Aquarium?

If you’ve read everything I’ve written in this article so far, you will probably already know that there is no single best-sized fish tank.

It can only be answered on a case-by-case basis. However, with that said there are certain rules which you can follow:

  • The larger the aquarium the easier it is to maintain. Think water management and also cleaning.
  • Don’t choose an aquarium which is only just big enough. You should always make sure to get an aquarium larger than needed so your fish flourish.
  • If you can’t provide a suitably sized aquarium, you should choose a different species of fish to keep.
  • The larger the tank, the happier your fish will be.

Where to Put Your Fish Tank?

When considering the size of your aquarium you also need to consider where the fish tank should be placed.

It’s no good having your fish tank in a large open room if the room itself isn’t suitable for a fish tank.

So what makes a room suitable?

  1. Low Light. Your aquarium shouldn’t be placed anywhere where direct daylight can shine onto it. So avoid windows, skylights, and this sort of thing.
  2. Low Noise. In a perfect world, your aquarium should be placed in a room on its own. However, sometimes this isn’t very realistic. Try to put your aquarium away from any noise source (TVs, Kitchen, Radios, Washing Machine, etc.).
  3. No Heat. As previously mentioned, maintaining the temperature of your water is one of the most important things you need to do. In order to maintain the water temperature, you need to also keep the air temperature around the tank stable. So avoid placing your aquarium near any source of heat.


I hope this article has helped you figure out what size fish tank you should get.

As you will now be aware, there is no perfect one-size-fits-all. You should use this article as your guide and make an informed decision after reading it.

Remember to also research the particular species of fish and find out its individual requirements as well. You can find our species guides here.

Finally, once you’ve got the tank, make sure don’t make these beginner aquarium mistakes.

Leave a comment below letting us know what sized fish tank you’re going to buy…

About Robert 468 Articles
Robert Woods is the creator of FishKeeping World, a third-generation fish keeper, and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America, and the Nature Conservancy.


  1. John O Herlihy says:

    you wrote a good piece. im still abit off which tank to buy. is 23 LRe enough, i think id like about 6 fish,im unsure which yet, i dont wan them to be stuck for anything

    • Robert says:

      Hi John,
      It all depends on which fish you want to include. Email me your wishlist and I’ll let you know how many of each you can stock.

      • kayla says:

        There’s some iffy information on this.Firstly you completely misrepresented the maryville study to “back up” claims that the researcher never concluded.Secondly fish still grow in smaller tanks multiple studies have disproven that small tanks stunt fish it’s simply not true.

  2. Eleanor says:

    Hi i have a 120 litre long tank with 7 cichlids in tank is two months old.Will be upgrading tank to 350 litre this week..also have a 30 litre Betta tank..I would like to get a 60litre tank for some sort of small schooling fish…would like stocking advice for 60litre and for community aquarium in the 120litre.and if I could add anything to the Betts tank.many thanks

    • Robert says:

      Hi Eleanor,

      Tetras, Swordtails and Platies are great beginner schooling fish.
      With regards to your Betta Tank, every Betta has a different temperament and whilst some will be OK with other fish, some will not. Harlequin Rasboras are a good option as they live in the same habitat in the wild.



  3. Antonina says:

    Thanks for all of the inportant information about fish and fish tanks, i loved it and had to translate it all in russian for my grandma and grandpa,i learned new things that i did not know before, THANK YOU VERY MUCH!!!!!! 🙂

  4. Mounica says:

    Hi I want to keep 9 goldfish… How much big fish tank I should buy

    • Robert says:

      Hi Mounica,

      Depending on the breed on goldfish you want, you should allow 20 gallons for the first one or two, and then 10 gallons for each on you add after that. These sizes are minimum – goldfish should have enough room to grow to their full potential.

      Thanks, Robert

  5. cameron says:


    If I plan on ultimately getting 3 guppies, 5 platies, 3 golden sailfin mollies, 1 swordtail, 1 brittlenose pleco, 2 corydoras catfish, several neon tetras and maybe electric blue ram/killifish later on, what size fish tank would you recommend I get?

    • Robert says:

      Hi Cameron, That’s quite a few fish! I recommend at least a 60 gallon tank. There are plenty of online calculators which you can check stocking levels with. I recommend using one of those.

  6. Lindsey Wallace says:

    What if I wanted 2 clownfish, 1 regal blue tang, 1 yellow watchman goby,1 cleaner shrimp maybe 2-3 snails? What size tank should I get? Will have a small anemone and maybe a coral

    • Robert says:

      Hi Lindsey,
      There are plenty of stocking calculators online which you can use to work out how many fish are suitable for each tank. Let us know what you decide.

  7. Abby says:

    I would love an opportunity to chat with you about an aquarium I am considering and get your thoughts/suggestions. I am curious about smaller fish that are comfortable with Bettas and how many Africa dwarf frogs would be happy living together. Would frogs and snails be a better option that fish? Your help is greatly appreciated!

    • Fishkeeping World says:

      Thanks for your question. It really depends on the individual nature of your Betta. We have an article here on the crowntail betta:https://www.fishkeepingworld.com/crowntail-betta/ which has a section on ideal tank mates. Let me know if there is anything else I can help with, Robert.

  8. Autumn says:

    Have 6 glofish and made the mistake of getting a starters tank.What size tank would you recommend?

    • Fishkeeping World says:

      Hi Autumn, do you have any other fish in the tank? If not, a minimum tank size of 10 gallons is fine. Thanks, Robert

  9. Carol says:

    I have 1 Rose Petal Male Betta and 1 snail and was told that a 3.5 gallon tank is a good size for 1 Betta and 1 snail. The Betta (Oscar) seems to be Ok in that siz of a tank with the Snail (S-Car-Go). What are your thoughts on that?

  10. Taylor says:

    hi, looking to start an nano aquarium but don’t know whether to go planted or not.

    • Fishkeeping World says:

      Hi Taylor, there are lots of benefits to having a planted tank but really it comes down to which you prefer the look of? Thanks, Robert

  11. Kiara says:

    I have had a couple of danios in medium sized tank for a while but I am considering upgrading.
    I would like to add more danios, some tetras maybe a loach and some other types to make a little ecosystem (with some live plants and all that)
    What sized tank would be needed to accomplish this?


    • Fishkeeping World says:

      Hi Kiara,

      A 30 gallon tank is a nice size to create a nice community of fish and plants. Not too large so that it take over either. Thanks, Robert

  12. Leila says:


    Im looking at getting one Neon Tetra, one Cherry Barb and one amber tetra. What size tank do you think that I will need

    • Ethan says:

      You should get at least 5 neon tetras, as they are schooling fish.

    • Ethan says:

      Also 5 amber tetras, I don’t know about the cherry barb but I would recommend at least a 12 gallon.

  13. Ethan says:

    Hey I have a 3-gallon tank with 1 male betta. I am thinking of upgrading to a 5 gallon. Should I get a 6 gallon instead?

  14. Kat Johnson says:

    Hi! So I’m thinking about getting 1 guppy. Are they ok by themselves or do they need company? What sized tank should I get? Thanks so much for this website its been really helpful

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