How Many Platies in a 20-Gallon Tank?

A 20-gallon tank is surely big enough to keep a nice group of platies, but how many can you safely leave in there? Well, a 20-gallon tank is suitable enough to contain 8 female platies or 13 male platies.

If you’re curious about the calculations we’ve made to get those numbers, stick around to find out how we did it. In this article, we’ll discuss everything you need to know about having platies in a 20-gallon fish tank so that you’re fully prepared for your journey as a fish parent.

Ready to dive in?

School of Platies

How to Determine How Many Platies in a 20-Gallon Tank Is Good Enough?

Of course, having 8 females or 13 males isn’t the only way to fill your 20-gallon tank with platies. You can also have a combination of both sexes in there. But how do you know the right number for each?

First of all, you must understand that, for each inch of a platyfish’s length, there should be 1 gallon of tank space. That’s the general rule most fish owners follow to find out how many platies to include in a certain tank size.

Second of all, keep in mind that the average length of an adult female platyfish is 2.5 inches, while the male is usually around 1.5 inches in length. So, based on these numbers, 8 females will require 20 gallons of water, while 13 males will need 19.5 gallons.

Now, if you want to have a mix of both sexes, you now have enough knowledge to calculate how many males and females to include in your fish tank. To help you out a little bit, here are a few male and female combination suggestions you may want to have in a 20-gallon tank:

  • 5 females (12.5 inches) and 5 males (7.5 inches), which equals 20 inches (20 gallons)
  • 6 females (15 inches) and 3 males (4.5 inches), which equals 19.5 inches (19.5 gallons)
  • 7 females (17.5 inches) and 2 males (3 inches), which equals 20.5 inches (20.5 gallons)

Can Male and Female Platies Be the Same Size?

Yes. Sometimes, you might stumble upon males that are longer than 1.5 inches. In this case, you must do the previous calculations based on the size of platyfish you have, and not the average values that we’ve mentioned.

As a result, the number of males in a 20-gallon tank can go a bit lower.

The same goes for females; your fish might grow to be bigger than 2.5 inches in length. Therefore, you should always look at the aforementioned numbers as guidance because they might not work out with everybody.

What Other Factors to Keep in Mind When Deciding the Number of Platies in a 20-Gallon Fish Tank?

If you’ll be keeping other types of fish in the same 20-gallon tank as the platies, you’ll want to think about more than just the platies’ sizes. Since other fish will enter the equation, you must make sure that all your fish will live in harmony in this tank.

This is why you should consider the following factors as well.


When it comes to food, platies tend to be fast-eaters. They’ll quickly gobble up any pellets you offer them, not giving their tank roommates enough time to feed as they please.

In this case, you might want to limit the number of platies in your tank, especially if the rest of the fish eat their food slowly.

Even if the other fish are ravenous eaters, it’s not a great idea to have too many platies either. This could mean more competition during meal times, which will end up with your platies feeling anxious and stressed.

Swimming and Hiding Places

Platies are also big fans of going for swims through the middle part of the tank, and they’re all about hiding in caves, plants, and amongst rocks.

Again, if they’re too many, they could occupy all the good swimming and hiding spots, leaving the rest of the fish unsatisfied. So, you mustn’t include more platies than necessary or the other fish won’t have enough room to swim or enjoy their privacy.

Orange Platy

Number of Live Plants

Platies like their fair share of aquatic plants for many reasons. They provide shelter, double up as food, and keep the water quality top-notch.

Now, the more platies you bring to the tank, the less they could benefit from the plants. And let’s not forget that other tank residents will need to take advantage of the live plants as well.

Therefore, it’s important to put the number of plants into consideration first before bringing your platies home from the pet store.

What Happens If I Put Too Many or Too Few Platies in a 20-Gallon Tank?

Both scenarios aren’t recommended because they end up with stressed-out, frustrated fish. If you want more details on how each case might negatively affect your platies’ health, here’s a quick comparison.

Having too many platies could lead to:

  • Overpopulation issues (platies breed fast)
  • Chemical imbalances in the tank water (more maintenance on your part)
  • An easier spread of germs and diseases

On the other hand, putting too few platies in a 20-gallon tank may cause:

  • Loneliness (platies are sociable fish)
  • Anxiety or depression
  • Lack of stimulation and activity, which could promote laziness

Have Another Tank Size You’re Looking for?

How Many Platies in a 5-Gallon Tank?

How Many Platies in a 10-Gallon Tank?

How Many Platies in a 29- Gallon Tank?

How Many Platies in a 55 -Gallon Tank?

To Wrap It Up

Wondering how many platies in a 20-gallon tank you should have?

After reading our article, you now understand how to calculate the number of platies to keep in your fish tank. A 20-gallon tank can take 10 platies; 5 males and 5 females. It might also house 13 males or 8 females.

It all depends on what you prefer to have in your aquarium, the availability of swimming space and hiding areas, and the behavior of other tank inhabitants. After taking all those factors into consideration, you should end up with your answer.