Last update: November 4, 2022

How Many Fish Per Gallon In Your Aquarium

Everyone is super-enthusiastic when setting up an aquarium.

Most want to create the best space where the pet fish can live without trouble.

Sure, thanks to technology and its homely applications, you can find a lot of gadgets that make your homely aquarium an impressive space — not just from the outside but deep inside as well.

Despite all this enthusiasm, many people reach a point of confusion when deciding how many fish per gallon is the best for your aquarium.

We cannot necessarily blame them, either. There is no proper science that dictates the perfect proportion between the number of fish and the amount of water.

Instead, you have to consider many factors, such as the accessories you put in, the possibility of fish diseases, and, of course, the types of fish you would like to have in the space.

We know it is a mouthful even to memorize these things. Therefore, we have prepared a guide on how many fish per gallon in your aquarium is the best option, answering some common queries.

How Many Fish Can I Have In My Tank?

fishes per gallon

In case you have not been expecting this, here you go: it is all relative.

There is no limit to the number of fish you can have in an aquarium tank. Depending on the size of the tank and the amount of water it can hold, you can have anywhere between 1 to 50 fish.

Well, as you know, that is just an estimate. Many aquarium enthusiasts use custom-built fish tanks to house double or triple that number. However, these experts do not just put more fish into the water as they please. Instead, the process involves a lot of planning from the very beginning.

Here are a few factors you should consider when deciding how many fish you can have in your tank.

The size of the fish is the most important thing. It would be best if you designed everything so that the fish has a sufficient amount of space to move around in the tank.

Similarly, the tank must handle all the waste from the fish, especially if you are dealing with a large one. In many cases, you can measure the number of fish based on the gallons of water.

For instance, there is a trendy 1-fish-per-1-gallon rule. However, as many aquarium enthusiasts would tell you, it has not been perfect.

You should also consider the accessories you would like to have in the aquarium. Depending on where you live and the access to water and everything, you may need a few tools.

You will have to ensure a steady O2 supply to the water and remove waste from the fish. For one, you can even try an aquaponics system. So, before you plan how many fish you want in the tank, you should see if you will have free space for all these elements in the end. Otherwise, you may have a less balanced livelihood for the fish, which is not cool.

Last but not least, you must consider the capacity of the tank, measured in gallons. We thought measuring in gallons would be the easiest way to help you answer the following questions.

How Many Fish Can I Have In A 2 Gallon Tank?

two gallons tank

As you know, most people start their journey with a 2-gallon fish tank. These tanks are not only compact but also easily manageable.

Even if you live in a space, you would not have trouble connecting the aquarium to the necessary outlets. Now, shall we answer the question?

Regardless of the type of fish you choose, you should add 1 to 3 fish into your 2-gallon fish tank. Choosing between 1 or 3 depends on a few things as well.

If you are dealing with small fish like guppies or small types of goldfish, you can always add two or three of them. On the other hand, if you want to accommodate large fish types and manage their systems better, you should start with one.

You must also dedicate space to live plants and other accessories. However, it would be best if you did not suffocate the fish on a safety-related note by adding too many live plants into the system.

Instead, you should make sure that the fish has enough space to move around even after setting up the plants/objects.

How Many Fish Can I Have In A 5-Gallon Tank?

five gallon tank

If you think you have enough experience with fishkeeping, you may want to upgrade to a 5-gallon fish tank.

While there is no problem giving more space to the one or three fish you had in the previous setup, you can always increase the numbers in this scenario.

Depending on the nature of the fish you want to grow, a 5-gallon tank can host up to 4 to 6 fish. In this case, you do not have to limit yourself to small-sized fish in the market. You can check out more extensive fish types, which would achieve great sizes over time.

However, make sure that the tank will have enough space for the fully-grown fish to move around. It would be best to judge the area based on how the fish looks when you buy and introduce them to the tank.

When you get a 5-gallon fish tank, you can experiment further with a few accessories. It would be best to consider adding a filtration system since you have more fish and fish waste to deal with. You must also accommodate some elements that allow the fish to interact.

How Many Fish Can I Put In a 10 Gallon Tank?

betta with goldfish

Let’s say you want to step up the game to a 10-gallon fish tank. It is also when you get enough space to customize certain things.

You can approach this extra space from two perspectives. One, you can use it to house as many fish as possible. Two, you can use the area to provide a more comfortable environment for the existing fish.

Going by the numbers, however, you can put up to 8 to 10 fish in a 10-gallon aquarium tank. However, we would not recommend adding 10 fish in a tank unless the fish are tiny and do not generate too much waste.

On the other hand, if you have chosen fish types that grow over time, you should limit the number to 8 or 6. There is no point in having an aquarium if the fish you have put inside cannot survive comfortably, correct?

We recommend adding fewer fish to a 10-gallon tank for another reason. Using the extra space, you can set up a suitable filtration system and add some live plants.

When you do this, you can reduce the frequency of maintenance. Over time, you will create a self-sufficient environment where your pet fish can grow.

As you can see, we do not quite follow the 1-fish-per-1-gallon system here. While it is a place to understand how things work, you should always expect the fish to grow larger and generate more waste. So, you should always choose a larger aquarium if you have a choice.

What About Filtration and Fish Stocking?


Now that we have found an answer to the how many fish per gallon question, shall we talk about filtration and fish stocking?

These may seem unimportant when you are growing only a couple of guppies or goldfish in a 5-gallon tank. However, when you increase the capacity and move to fish that generate a lot of waste over time, you need dedicated filtration options.

Filtration is an area where you should not overdo things. It is great to have a system that removes waste from water and maintains a good proportion of oxygen, but that is it.

You should also check if the said system can maintain a good harmony of good bacteria in the tank. If it cannot, you may need something else over time.

Instead of fixating on a singular filtration system, you can consider getting aquarium plants and rocks, as we said. These elements will provide enough space for the fish to hide and stay away from the diseases that may affect specific fish types.

Fish Stocking is even more critical if you ask us. At its core, fish stocking deals with the type of fish you will be putting in the tank. You have to design the tank strategically so that the fish will have enough space for swimming.

You should also avoid putting aggressive fish types with peaceful ones. Otherwise, your aquarium would become a pool of dead fish before you realize it. If you do not get the ideal kind of water in your area, you should check the aquarium for the chemical levels.

You should ensure that the problems in water do not affect even a single type of fish in the tank. As you can see, fish stocking is a time-consuming process indeed.


As you saw, the answers to how many fish per gallon questions are not absolute by any chance.

We do not want you to follow these suggestions as they are presented either. Instead, you should give enough space to aspects like stocking, filtration, chemical levels, and tank capacity before introducing the first fish to an aquarium.

Ian Sterling

Ian Sterling, founder of, began his aquarium journey over 30 years ago, driven by a deep fascination for fish and their diverse personalities. His website,, is dedicated to making fishkeeping accessible and enjoyable, offering beginner-friendly guidance, expert insights, and a community for aquarists to connect and share experiences.

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