How Many Guppies in a 10 Gallon Tank? 20 Gallon?

As a beginner fish keeper, you are going to want to start out with easy fish; and if you aren’t a beginner, you probably know already that guppies are enjoyable and easy to care for. Choosing which size fish tank to keep them in, however, can be difficult to calculate if you don’t know what to consider.

So, if you need the answer for how many guppies in a 10 gallon tank, you have come to the right place. Let’s cover how to determine the amount of guppies, as well as how to optimize the fish tank so your fish can thrive.

What You Should Know About Guppies

Color Form:Every color imaginable
Lifespan:Up to 2 years
Size:0.6 – 2.4 inches
Minimum Tank Size:5 gallons
Tank Set-Up:Freshwater, plants and substrate
Compatibility:Other peaceful community fish

The guppy is a tropical fish native to the freshwaters of South America. There are over 300 different kinds of guppies, and they all have a variety of sizes, colors, and fins. In 1866, an explorer in Trinidad, a man named Robert John Lechmere Guppy, discovered the fish and took samples back to a British museum, where it received its first scientific name.

Guppies are also known as Rainbow Fish, because of their vibrant colors of fancy fins, and Millions Fish, because of their exponential reproductive rates.

Aside from looking fabulous in tanks, guppies have also served the waters of Asia as part of a mosquito control program. But their release in the wild had a negative impact on other native fish, so the program stopped. In an aquarium, though, guppies are peaceful, friendly fish who are very active. If your guppies hide, it means that they are stressed.

Speaking of colors, guppies are indeed Rainbow fish for a reason. They can be solid or have a pattern, such as:

  • Cobra: rosettes and vertical bars
  • Tuxedo: two different colors on the front and back halves of the fish
  • Snakeskin: a chain-link pattern

And their tails can have the following patterns:

  • Mosaic: irregular, interconnected spotting
  • Grass: tiny speckles
  • Lace: web-like
  • Leopard: spotting that look like a leopard’s

Guppy tails can also have various shapes, such as:

  • Fan
  • Triangular
  • Sword (double, top, or bottom)
  • Spade
  • Rounded
  • Spear
  • Lyretails
  • Flag

How Many Guppies In a 10 Gallon Tank?

Before we talk about how many guppies can fit in a 10 gallon tank, there is something worth prefacing. First, you should know that a 10 gallon tank is not as large as it seems, but it is a great option for new aquarium owners. A 10 gallon tank can be the home of many fish, and if you plan out the layout carefully, the aquarium will be a beautiful microcosm of life.

But, 10 gallon tanks are not meant for beginners, because a small tank is less forgiving in terms of mistakes. That is why you have to first know the temperaments and ideal habitats of the fish you want. Otherwise, you might see premature death.

With that in mind, let’s talk about how to calculate how many guppies in a 10 gallon tank.

There is a popular belief that for any fish that is 3 inches or less when full grown generally needs 1 gallon per inch. This means that if you have 10 fish all measuring 1 inch in length, you can fit 10 in a 10 gallon tank.

Easy, right?

Well, not necessarily. Fish do not grow uniformly. Some fish will stay small while others might shock you with how big they get in the proper conditions.

Another thing to consider is that a 10 gallon tank does not hold 10 gallons of water. Gravel, filters, decorations, and live plants all take up space. You may end up with a volume of 7-8 gallons.

This means that, since an adult guppy averages around 1.5 in (3.8 cm) in length, without their tail fins, then 10 gallons of water could fit around 7 guppies. Avoid adding more than 10 guppies.

Gender-Based Restrictions

Another thing to consider when buying guppies for a 10 gallon tank is that some guppies might not be full-size at the pet store. This means you need to consider extra growth within the tank. A 10 gallon tank can hold a group of guppies that total 10 inches in length, so if you have two males (about 1-2 inches) and 1 female (about 2 inches), you have 5-6 inches in length, which gives your fish more than enough room.

Of course, keeping male and female guppies together is not recommended, since they will have babies…and potentially overload your tank.

Is It Possible To Add More Guppies To a 10 Gallon Tank?

Some people like the sight of a crowded fish tank. Others want to watch the kaleidoscope of guppies swimming around a smaller tank. As long as your fish are happy and healthy, you could try fitting more guppies than what the rule of thumb advises by working with total water volume.

Here are some tips:

  • Switch from an internal filter to an external one
  • Add live freshwater plants to the tank, including fast growing floaters
  • Avoid gravel substrate—try sand–but don’t get rid of it entirely
  • Reduce feeding to once every other day

Pro Tip: Change 30-50 percent of the aquarium water weekly

How Many Guppies In a 20 Gallon Tank?

If you have a 20 gallon tank, you can certainly add more guppies or even some tank mates into the mix. When calculating how many guppies fit in a 20 gallon tank, just remember the rule of thumb.

That means you divide 20 by 1.5 inches to get 13.3. Therefore, you can fit anywhere from 12-19 guppies, depending on their gender and size. Again, you also need to keep in mind the layout of your aquarium and the total water volume available.

A 20 gallon aquarium with a massive decoration in the middle may actually only have 15 gallons!

What If My Guppies Have Babies?

As mentioned previously, if you plan on keeping both male and female guppies together, you can count on seeing baby guppies. For some people, this could be an incredibly exciting event. However, you need to remember that those babies are going to need additional care.

Additionally, baby guppies cannot be kept in the same aquarium as older fish. You will either need to separate them, donate, or sell them.

If you don’t want surprises, then it is best to keep your male and female guppies separated from the start.

Tank Maintenance

Both 10 and 20 gallon guppy tanks are not that difficult to care for, as long as you do not overcrowd the tank. Your guppies will need a water temperature of around 72-80 degrees F. Feed them a balanced diet to make sure they have enough vitamins and minerals. Change the water often.

Keeping Live Aquarium Plants With Guppies

Like other species of fish, guppies love grass and hiding in decorations. Apart from providing entertainment, live plants add a sense of realism to the aquarium. Another benefit of aquarium plants is the removal of toxins in the water and oxygenation. Naturally, you don’t want to overload your tank with one too many plants, so you need to choose wisely.

Some plants are better for guppies than others, including:

  • Guppy grass – also known as najas grass
  • Hornworts
  • Wisteria
  • Java fern
  • Watersprite
  • American waterweed
  • Amazon sword

The above listed plants are all easy to care for, grow relatively quickly, and add another array of color and intrigue to your tank. Together with guppies, you get a beautiful display. And what’s better: by providing plants, you ensure your guppies stay happy!


The colorful and energetic guppy is an ideal fish for a beginner fish tank, as well as more experienced hobbyists. Not only are these fish hearty, but they are easy to care for—as long as you give them plenty of nutrition and space to swim around. For this reason, you should keep around 6-10 guppies in a 10 gallon tank or 12-20 in a 20 gallon tank. Refer back to this article if you need more information when organizing your 10 or 20 gallon tank.

Share on facebook
Share on twitter
Share on pinterest
Share on email
Share on print

Leave a Comment

Your email address will not be published. Required fields are marked *