How Many Goldfish Can Fit in Per Gallon Tank?

One of the most beautiful creatures of this world is goldfish. There are probably very few people who didn’t keep goldfish as a pet once in their life. So are you are someone who just bought a goldfish or thinking about buying one? Then the widespread query how many goldfish per gallon tank might have come across in your mind at least once.

How Many Goldfish Per Gallon Tank?

The answer to the question is not so simple; this is why you need to know in detail.

To be honest, like a goldfish owner, you should be cautious about the size of the tank.  The tank size is important because the wrong choice of a tank can make your goldfish stunted. When the goldfish becomes stunted, it’s a sign that it will be dead soon.

Goldfish in a small bowl is a common scenario. You might also think about getting a bowl for your goldfish. But do you know even though it looks beautiful in the container, but it is not happy at all. A goldfish can grow up to six to eight inches, so it needs extra space. And if you can’t provide enough space for the goldfish, it becomes stunted.

You do not need a goldfish tank size calculator in real to get the exact measurements. One gallon of water per inch fish is the general rule of calculating the size of the goldfish tank. This simply means when the goldfishes are small, and one inch in size, one gallon of the tank is enough for it. But with time when it will grow, you need to shift it into a larger tank.

Now let’s dive into the details of the larger tanks.

How Many Goldfish in 10 Gallon Tank?

10 to 20-gallon aquariums are considered as the starting tank when keeping goldfish as pets. These tanks are not recommended for long term use. One inch of fish per one gallon is the general rule used to determine the tank size or the number of goldfish to be kept in a tank of a particular size. As per this rule of thumb, two to four small goldfishes can be kept in a 10-gallon tank. It should be remembered that goldfishes grow quicker than other fishes. But they will not get matured and be of proper size unless they are kept in a larger tank. However, if you follow this rule, you have to keep a record of the sizes of the goldfishes regularly. Common goldfish can easily grow up to 10 inches and fancy goldfish usually reach 8 inches in length. Some goldfish have grown even bigger.

Some fish hobbyists recommend putting a single goldfish in a 10-gallon tank so that it can grow up in a proper environment.  So it is better to keep them in a larger tank from the beginning to avoid overload of fish waste, less room for the fish, stress on the fish, polluted water, disease, and death. Usually, tanks smaller than 10 gallons are not used for goldfish due to lack of inadequate room for the fish.

How Many Goldfish in 20 Gallon Tank?

The answer to this question is somewhat tricky.  Two common goldfish can be kept in a 20-gallon tank. But two fancy goldfish cannot be kept in a 20-gallon tank as they require more space. So the minimum recommended tank size for keeping one fancy goldfish is 20 gallons. If you wish to keep more than one fancy goldfish, you have to add an extra 10 gallons. Thus you can put two fancy goldfish in at least a 30-gallon tank. 20-gallon is for the first fish and 10 additional gallons are for the second fish.

If you want to add fish of other breeds, you have to calculate their size in addition to the goldfish. However, you should be prepared to buy a larger tank as they grow. If you are interested to keep your goldfish healthy and happy, you should follow this another rule of thumb: one goldfish requires at least 20-gallons of water. So that means two healthy goldfish can live healthily and happily in a minimum 40-gallon aquarium.

5 Reasons To Keep Goldfish In large tank:


  1. Goldfishes are bulky in shape, and because of this, it needs more oxygen in comparison with other fishes. When goldfish grows, it becomes four sizes bigger then the size it was, and at that time, it will require more oxygen. Thus you should provide the fish enough space; otherwise, it will always be gasping for breath at the bottom of the tank.


  1. A goldfish body is made to grow at least 6-8 inches. But unfortunately, most of the pet goldfishes never get the chance for this. As the pet owners often fail to understand the importance of the large tank. When you keep your goldfish into a tank with enough space, it will be able to grow correctly. If you can’t provide enough space, it becomes stunted and sick. In this way, the life span of the goldfish will be shortened.


  1. Goldfishes owners who have kept it in a small aquarium often change the water to keep it clean. But goldfish is a creature that gets shocks with constant water temperature changes. It disturbs the goldfish, even more, when you do it in a small aquarium. The reason behind this is when you change the water in a small container, it cools or heats quicker, unlike large tanks. In large tanks, there is more water and it slowdowns the temperature changing process. So use enough spacious containers instead of small bowls to keep your goldfish away from shock.


  1. A full water tank never looks good, no matter how beautiful the fishes are. It is also unhealthy as lots of fishes in a small container will make the water dirtier as soon as possible. Moreover, goldfishes do not like to stay in an overcrowded tank. They get aggressive when the tank is too much crowded with fishes. If the goldfishes start with fighting with each other, they might suffer from wounds and fungal infections.


  1. No one likes being all alone the whole day, and in the case of goldfish, it is the same too. Just like us, they feel lonely too. When you keep one single goldfish in a single bowl, it would not be happy and cheerful. Thus getting a large tank to keep at least two fishes is a must to keep your keep goldfishes happy.

Here are few Goldfish tank size myths that you should avoid:

Believing is an excellent practice, indeed. But sometimes believing in wrong information regarding your goldfish tank can make responsible for its death. That is why you should be aware of the common myths related to the goldfish tank.

  • A small bowl is enoughThis is one of the most common myths for the goldfish tank’s size. A bowl is never enough for it. Goldfish will simply outgrow the bowl, and it will be stunted if it does not shift into a bigger tank.
  • Goldfish grows according to the size of the tankThis is wrong, because if you properly take of your goldfish and provide it with all the necessities. Then it will never stop growing. It’s just one of the techniques of preventing the growth from avoiding a larger tank.
  • Goldfish never lasts longIf your goldfish dies in a few years, then the only reason behind it is the size of the container. When the goldfish becomes stunted due to insufficient space, it’s a hint that it is sick. And eventually, a sick goldfish without any care would not last long, just like humans.


There you go; I have gathered all the necessary information that anyone needs to take into account before buying a water tank for their precious goldfish. I hope now, after reading our piece of writing all your confusions and queries about how many goldfish per gallon of tank is clear. Hope you have a great time in nurturing your goldfish. Thank you!

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