How Many Guppies Per Gallon? One Rule Fits All

Guppies are vibrant fish that can twinkle in every corner. People like to raise them in groups to watch the beautiful tiny spots moving. But how many guppies per gallon is enough?

The right number of guppies in your tank differs depending on several factors. We will give you the best answer below. Let’s join us!

How Many Guppies Per Gallon?

An adult guppy requires at least a gallon of water. The best calculation is one gallon for one inch of fish.

The average length of adult guppies is around two inches. They need to live in groups for the best development. Hence, you need a 10-gallon tank for five to ten fish.

You need to take two steps to find the optimum number of guppies in your aquarium.

Measure the tank

Measure your tank’s size first. Remember that you must calculate how much water the container can hold once fully filled.

Apply the formula

Now, you can determine the maximum number of guppies to add by using the rule of one gallon per guppy.

A group of guppy fish would live well in a 40-gallon aquarium. The tank should be able to hold water for 20 fish, plants, and decorations.

Consider the gender of your pets as well. To keep the tank harmonious, set the ratio at two females to one male.

Tank size The ideal number of guppies
5 gallons 3
10 gallons 6
15 gallons 9
20 gallons 12
40 gallons 20

Can You Keep Only One Guppy In A Tank?

Theoretically, it’s OK to raise only one guppy in an aquarium. However, people like to keep them in groups because these fish get used to sharing a home in the wild to fight against predators and seek food.

As you can see, they coexist with their mates for two reasons: Food and predators. Hence, raising one guppy is possible if:

  • The tank is safe and predator-free, so your pets don’t have to battle with attackers.
  • You can feed your fish regularly. As a result, they won’t need to search for food in groups.


You can keep one fish in a tank

Problems Of An Overpopulated Guppy Tank

Why do you have to give your pets the right tank size? Because they need a comfortable space to live. Otherwise, overpopulation leads to severe problems.

Shorter lifespan

Living in a small tank will cause growth stunting, muscular atrophy, spinal distortions, and other health issues in young fish. A fish that becomes stunted will therefore have a shorter lifespan.


Imagine having to share a room with someone else. Having roommates may be fun, but eventually, you’ll get tired of them.

Such a problem occurs when several guppy fish get trapped in a small tank. They have to fight for their space all day.

Lowered water quality

The balanced nitrogen content plays a vital role in maintaining a healthy tank.

However, when there are more fish, there will be more waste, increasing ammonia levels.

The water quality can suffer from overpopulation. As a result, you’ll need to change the water and clean the gravel frequently.

Stress and diseases

Fish stress might result from a crowded habitat. When feeding guppies in a tiny tank, you should consider this factor.

A healthy fish should be happy and comfortable in its surroundings. Good conditions give them stronger anti-illness defenses.

Otherwise, your fish will face stress, behavioral abnormalities, and fungal infections.

Tips For Raising Guppies

Tank size is essential for guppies. Besides, you should also pay attention to other factors, such as:


If you are raising a lot of guppies in your aquarium, you will need to give them enough food. Aggression during meal times can result from constantly feeding your pets less food.

A common rule to remember when determining how much food to give your fish is that you should only give them as much as they can eat in one minute.

You can learn more feeding tips right here:

Female-male ratio

As discussed earlier, you need to maintain a ratio of female to male guppies 2:1.

If there are more males, the females will become harassed by their male mates, leading to a shorter lifespan and more stress.

Add hiding places

Even if you keep the gender ratio the same, male fish constantly chase and bother the females. So how to solve this problem?

You should give your guppy tank lots of hiding places. Your pets can use live plants and decorations to avoid contact with others. 

Use excellent filter media.

Sponge filter media won’t work in an overcrowded aquarium. So, you need a powerful tool as the filter performance matters.

You also need biological filter material aside from the standard sponge filter.

It will provide a huge area for beneficial germs to break down toxic compounds like ammonia and nitrite.

Meanwhile, the sponge filter is in charge of trapping the heavy muck.

Perform frequent water changes

Care and attention to the tank are essential no matter how many fish you raise.

You need to perform water changes more frequently for a more crowded tank because the waste can accumulate more quickly.

Weekly water changes should suffice if you install a decent filter and filter media.

We recommend performing 30 to 50% water changes to prevent mishaps.

Thoroughly clean the filter as well. It would be best to give it a treat every other week for the best result.

Avoid washing the filter media with tap water because chlorine will destroy all of your beneficial microorganisms.

Also, avoid keeping the biological substrate dry for an extended period. Otherwise, it will eliminate the friendly bacteria.

The water must be clean


The rule of thumb for choosing the right number of guppies is one fish inch – one gallon. Please give them a suitable space so your pets can swim freely and live healthily.

Also, avoid overstocking your aquarium. Your fish will seriously suffer from the reduced water quality and aggressive tank mates.