HomeAquarium & MaintenanceHow Many Guppies In A 20 Gallon Tank? A Complete Guide!

How Many Guppies In A 20 Gallon Tank? A Complete Guide!

You may be curious about how many guppies in a 20 gallon tank to avoid overcrowding and ensure their health. Overcrowding in an aquarium can lead to fierce competition for resources and can potentially harm your guppies.

In this guide, we’ll cover everything you need to know about the right number of guppies for a 20-gallon tank, the factors that influence this decision, and the consequences of keeping too many guppies in a tank. Not only will this information help your guppies thrive, but it will also help you become a more knowledgeable and responsible guppy caretaker.

Overview 20 Gallon Tank

A 20-gallon aquarium is a favored choice among aquarists. Its size strikes a balance, providing ample space for diverse fish species while remaining manageable in upkeep. When considering guppies, a delightful and vibrant species, a 20-gallon tank can comfortably house 12-16 females or 10-12 males.

This allocation takes into account the size disparity between the genders; females typically reach about 2 inches, while males mature to approximately 1.4 inches.

20 Gallon Tank
20 Gallon Tank

How Many Guppies Can Fit in a 20 Gallon Tank?

A 20-gallon tank can comfortably accommodate 10 to 12 guppies without risking overcrowding or related issues. These small, vibrant fish require adequate space to swim and flourish. Cramming them into a compact tank can hinder their growth and dampen their spirits.

For every 2 gallons of tank water, experts suggest housing one guppy. Gender plays a role in this equation. Female guppies are typically larger than males, so you might want to limit the number of females if space is a concern.

How many guppies in a 20 gallon tank
How many guppies in a 20 gallon tank

If you’re new to the world of fish-keeping, it’s wise to start with a smaller number of guppies. This allows you to observe their behavior, breeding patterns, and growth. Also, keep in mind that other tank elements like live plants, ornaments, and substrate can consume around 5 gallons of space.

Guppy Gender

Gender plays a pivotal role in the world of guppy care, and for those new to the hobby, distinguishing between the two can be a challenge. Thus, it’s crucial to gather knowledge before introducing them to your tank. Here’s a closer look at the nuances of guppy genders:

Female Guppies:

  • Body Structure: Females tend to have a more rounded shape and generally surpass males in size.
  • Size: On average, they are notably larger compared to males.
Female guppy
Female guppy

Male Guppies:

  • Body Structure: Characterized by their slender and elongated forms.
  • Color Palette: They truly stand out due to their diverse and brilliant colors, particularly in the tail region. Their shades are not just varied but strikingly intense.
Male guppy
Male guppy

For enthusiasts keen on introducing a burst of color to their tanks, male guppies are the ideal choice. A 20-gallon space can accommodate up to 13 males. Conversely, if you’re inclined towards the fuller-bodied female guppies, a group of ten is recommended. For a balanced mix of both genders, housing 10 to 11 guppies would be optimal.

Guppy Size

The size of a guppy depends on two things: whether it’s a boy or girl, and how old it is. Are you buying young guppies or older ones? Remember, guppies grow up in about six months.

A grown-up maleguppy can be as long as 1.8 inches, while a female guppy can be between 2 to 2.5 inches. If you’re buying young ones, think about having another tank ready. You might need to move some of them there when they get bigger.

Guppies change in size as they grow. If you buy big guppies of both male and female, they will soon start having baby guppies. So, you’ll need another tank for the babies or more space.

Guppy size
Guppy size


Guppies give birth to live baby fish, not eggs. When you have both male and female guppies together, they will have babies very fast.

Here’s a thing: baby guppies can’t be in the same tank with grown-up guppies. So, you need to think ahead! You can give the baby guppies to friends, sell them, or set up a new fish tank. Remember, a new tank with plants and decorations can cost more, but maybe you’d like having more tanks.

If you keep male and female guppies in one tank, they’ll keep having babies. Soon, your tank will be too full, and all the guppies will be fighting for food and space.

To avoid this, you can:

  • Keep the boy and girl guppies in separate tanks.
  • Choose only one type (all boys or all girls) if you have a small budget or not much room.
  • Have more boy guppies than girl guppies. They might still have babies, but not as often.
Guppy breeding
Guppy breeding


If you put too many guppies in your tank, it can cause problems. These are some issues you might face:

  • Not enough oxygen for the fish.
  • Too much waste, like ammonia.
  • Stressed-out fish.
  • Slow growth.
  • Fish fighting each other.
  • Hard to keep the water clean.

Remember to check how many guppies are in your tank. By doing this, you can keep your fish healthy and happy. 

Also, a tall fish tank isn’t the best choice. Why? Because it doesn’t have a lot of surface area for oxygen to get in. If you have a tall tank, you might need something to help add more air. With the right amount of oxygen, a tank can have about ten guppies.

Guppy overcrowding
Guppy overcrowding

Other Fish

Guppies get along well with many other fish. So, what fish can live with guppies in a 20 gallon tank? Some compatible matches include Platies, Cory catfish, Mollies, Betta Fish, Cardinal Tetra, Honey Gouramis, Harlequin Rasboras, Otocinlus catfish, and Dwarf neon rainbowfish. But before you add new fish, make sure they’re a good match with guppies so they don’t fight.

If you have a 20-gallon tank and want to have both mollies and guppies, remember this: You can have up to four to six molly fish. A good mix is one molly for every two guppies. And just to give you an idea, an adult guppy is about 2.5 inches while a molly can grow to 4.5 inches.

>> Explore more: Best 10 GALLON FISH TANK Reviewed In 2023 (Top 5 Picks)

Factors to Consider When Choosing the Number of Guppies 20 Gallon Your Tank

When setting up a 20-gallon tank for guppies, several considerations come into play to ensure a healthy environment for the fish. These factors determine not only how many guppies your tank can comfortably hold but also contribute to their overall well-being.

The size of the guppies

The size of your guppies matters a lot. Adult guppies can be around 2 inches long, but younger ones are smaller. If you’re adding young guppies, you can have more of them in the tank compared to if you’re adding fully-grown ones.

The amount of plants in the tank

Plants aren’t just for decoration. They help clean the water and give guppies places to hide. If your tank has many plants, you can keep more guppies. The plants will help keep the environment healthy for them.

The amount of plants in the tank
The amount of plants in the tank

The filtration system

Don’t forget about your tank’s filter. A strong filter keeps the water clean by removing harmful stuff. If your tank has a high-quality filter, it can handle more guppies.

Tank Maintenance

Consistent tank upkeep is crucial, and the frequency often depends on how many fish you house. More fish typically means more frequent cleanings, which can range from several days to weekly.

Managing a 20-gallon tank can be straightforward, especially if you’re housing no more than 13 guppies. Aim to keep the water temperature steady, between 72 to 82 degrees Fahrenheit. Feed your guppies a balanced diet, and be cautious not to overfeed them.

Regularly check your filter to ensure it’s running smoothly. Recognizing when it’s time for filter maintenance can significantly impact the health of your tank. Keeping the appropriate number of fish in your tank not only simplifies maintenance but also ensures a visually stunning aquarium.

Tank Maintenance 
Tank Maintenance


In conclusion, determining How many guppies in a 20 gallon tank is essential to ensure a healthy and comfortable environment for your aquatic pets. The size of the tank, coupled with other vital factors, plays a pivotal role in their overall well-being.

We hope this guide has provided clarity on this topic. For more insightful tips and guides on aquarium care, don’t hesitate to explore more blogs from National Park Aquarium. Dive deep into our content, and let’s keep our aquatic friends happy together!

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Kevin Mills, the founder of Nationalparkaquarium.org


-- Founder --

I'm Kevin Mills, the founder of Nationalparkaquarium.org, where I share my deep passion for aquariums and aquatic life. With over 20 years of experience in fishkeeping, covering everything from tending to saltwater and freshwater tanks.

Kathleen Wood


-- Interrogator --

Kathleen Wood, a seasoned marine biologist, possesses a wealth of knowledge and experience in her field. Her research on tropical fish biodiversity spans over three decades, and she has contributed numerous scientific papers on aquatic life.