How Many Guppies in a 20 Gallon Tank?

The ideal number of guppies in a 20 gallon tank should be between 8 and 12.

If you’re thinking of getting guppies for your tank, that’s a great choice! Guppies are very peaceful and appealing to the eye, which is what most of us look for in aquarium fish.

However, This tropical freshwater fish is accustomed to swimming freely and riding currents. So, it won’t reach nicely if you restrict its movements by overcrowding the tank. Stick around to learn how to keep your guppies in the perfect ratio!

How Many Guppies in a 20 Gallon Tank?

In a 20-gallon tank, you should keep between 8 and 12 guppies. Yes, guppies are tiny, but they are very active, so to create a healthy environment for them, you’ll need to figure out how many you should keep in one tank.

“One inch per gallon” is a simple rule that helps with calculating the number of guppies that each tank should include. To explain this rule, a normal guppy’s size ranges from one to two inches in length, so you’ll need to put a gallon of water for every inch.

However, the gender of the guppy plays an important role in this rule because male and female sizes differ.

Orange Black Guppy and Silver and Gold Guppies

How Does Gender Affect the Calculation Rule?

We’ll go over the ideal ratios for putting females, males, and mixing both genders in a 20-gallon tank.

First, let’s assume that the other complementary items added to the tank, such as gravel and plants, will occupy five gallons.

Only Female Guppies

The size of a female guppy ranges from 1.2 to 2.4 inches. In that case, a 20-gallon tank should contain 8 to 10 female guppies.

You can identify a female guppy by its curved body and pale colors, usually silver or pale gray.

Only Male Guppies

Male guppies are smaller than female guppies, measuring between 0.6 and 1.4 inches in length. Having that said, you can keep 10 to 12 male guppies in a 20-gallon tank.

Unlike female guppies, male guppies have straighter bodies and much brighter colors. Those vibrant colors are to attract females to mate when it’s time for breeding.

Mixed Guppies

If you’re going to keep male and female guppies in the same tank, stick to a male-to-female ratio of 1:2. This means that you should have one male guppy for every two females.

This ratio is intended to keep a peaceful environment as females are less territorial than males. So, the ideal ratio for a 20-gallon tank is four males to eight females for a total of 12 guppies.

Can Guppies Mate and Overpopulate the Tank?

Yes, that’s something that can happen if you keep both genders in the same tank. In that case, you’ll want to get another tank so you don’t end up with a too crowded one.

Keep in mind that, despite being a nonviolent breed, guppies engage in filial cannibalism. This type of cannibalism involves them eating their own fry.

Although the cause of this phenomenon is unknown, several possibilities have been proposed, including:

  • When adult guppies are hungry, they consider fry their food.
  • Female guppies can consume their offspring to retain their fat storage after birth.
  • To get rid of the weak offspring
  • Female guppies may experience psychological stress after giving birth, leading to them eating their offspring.

To keep adult guppies from eating the fry, keep them apart until the fry has grown.

On the other hand, if you don’t want your guppies to reproduce, I strongly advise you to separate males and females from the start. Females can store male sperm for several spawnings even after being separated.

Intense Orange Fancy Guppy in Front of Plants and Gravel

What If There Are Too Many Guppies in the Tank?

Guppies are a small, low-maintenance breed that is popular among beginners. However, you don’t have to be an expert to realize that overstocking them will cause serious problems.

That’s especially when you mix both genders in the same tank, as guppies are prolific breeders, which means they produce many offspring.

One of the major drawbacks of an overcrowded tank is that it creates an uncomfortable environment for your guppies to live in. Furthermore, it jeopardizes their health.

Uncomfortable Environment

Guppies are energetic and active swimmers, so whatever tank they’re kept in should be accommodating.

The first thing you should consider when caring for a guppy is to try to replicate the environment in which they once lived.

That is to maintain their health and reduce the factors affecting their psychological well-being. Guppies may show the following symptoms in cases of overpopulation:


Guppies are freshwater fish, so when they don’t have enough space to swim freely, they become stressed. Increased stress has an impact on their immune health, which increases their risk of disease.


Whether the tank has solely males or only females, there will be hostile energy as a result of guppies stressing out.

Of course, if the tank contains both genders, the male’s competitiveness and frustration will increase due to a large number of competitors.

Increased Waste

As the number of guppies grows, so does the amount of waste produced, which can lead to ammonia poisoning.

Ammonia levels rise as a result of bacterial build-up and as a byproduct of the protein-building process in fish.

Although the tank probably has a filtration system, it will eventually be unable to keep up with the waste produced.

Besides, you’ll get tired of the maintenance process as you’ll keep seeing waste accumulate even if you’ve recently changed the water in the tank.

Reduced Oxygen Level

Guppies require oxygen to survive. They breathe by sucking the oxygen out of the water using their gills.

When a large number of guppies are housed in a small tank, they won’t receive enough oxygen to stay healthy.

Both of these factors will have an effect on guppies, which can take any of the following forms:

  • A weakened immune system
  • Inability to develop normally

Have Another Tank Size You’re Looking for?

How Many Guppies in a 3-Gallon Tank?

How Many Guppies in a 5-Gallon Tank?

How Many Guppies in a 10-Gallon Tank?

How Many Guppies in a 29-Gallon Tank?

To Recap

Guppies are lively creatures, and we all enjoy watching them do their thing. To find out how many guppies can fit in a 20-gallon tank, just follow the simple rule outlined here.

In addition to that, make sure you’re following the guidelines that’ll ensure they live a healthy and comfy life. In the end, you’ll be happy to see them thrive in your tank.