How Many Guppies Per Gallon? How Many Guppies In A Ten Gallon Tank?

How many Guppies per gallon
Guppies are high-spirited species, are active and joyful; perfect beginner’s species. They are small fish and don’t occupy huge space. If you are a novice aquarist and contemplating the idea of having an aquarium tank with Guppies in it, you for sure ask the question, how many Guppies Per Gallon of water can you keep?
Although Guppies are small fish, they need some space to swim around; confining them in a small bowl or a tank can oppress them and impede their mood and healthy growth.
Therefore, to enjoy the experience of fish-keeping, you would want to choose the right number of specimens for your tank or bowl. Let us see how many Guppies per gallon you can keep.

How to Calculate the Number of Guppies for an Aquarium Tank?

Guppies are cute tiny species; both neophytes and expert hobbyists love them. They are easy to care for and friendly species to pet.

However, their deceiving small size can often make you think that you can confine as many specimens in a small bowl or a tank. But hold on! Never commit this mistake!

Just because guppies are small, it does not mean that they do not need much space. Instead, they love sufficient space to hover around freely and swim in a large area like anyone else.

The thumb rule for deciding the number of specimens in a tank is 1-gallon water per inch (2.54 cms) of fish; this calculation refers to their fully grown size the species achieve as an adult. Usually, a fully grown male Guppy reaches 1.5 inches (4 cms) long, and a female guppy gets 2 inches (5 cms). Going by this standard calculation for one guppy, you need to have at least a 2-gallon capacity of water. In a typical 10–20-gallon aquarium, you can add 5-10 guppies to offer them enough space to swim and thrive. 

Factors Determining the Number of Guppies in an Aquarium

Guppies are agile and dynamic schooling species. They are beginner’s boon; they are hardy and easy to care for. It’s best to start with a school of 4 to 5 fish; from there, you could scale it up as you learn and experience different aspects of maintaining a Guppy Tank.

It is then time to calculate how many guppies per gallon you can add to the tank. When you buy them at the pet, they are most likely to be tiny fish; so, while calculating the space requirement, always consider a fully grown adult Guppy’s size, i.e., approximately 1.5 inches (3.8 cms) for a male Guppy and 2 inches (5 cms) for a female Guppy.

For 5 Guppies, you would need approximately 10 gallons (38 liters approx.)of water; To hold 10 gallons (38 liters approx.) of water, you would need more than a 10 gallon (38 liters approx.). For instance, if you have a 10-gallon aquarium, its water volume capacity will be around 7-8 gallons (26 to 30 liters). A wholly set up tank has its substrates, decors, plants, diffusers, filter, etc., occupying specific space, thereby reducing the room for the water.

Next, based on the aquarium’s water holding capacity, use the thumb rule of 1-gallon per every 1 inch (2.54 cms) of Guppy to calculate the maximum number of fish you can keep in it; going by this calculation, you would need a tank that can hold at least 10 gallons (38 liters) of water for a school of 5 Guppies. Remember, Guppies are prolific breeders; your school of Guppies will multiply before you know it; be ready to house them in a bigger tank.

Ensure maintaining the sex ratio at 2 to 3 females for every male Guppy; besides, two male Guppies can be aggressive to one another.

In evolution, we know the environment molds the organisms living in it and their behavior; however, some studies show these tiny creatures can quickly evolve and shape their tank environment in which they are residing. 

Related Readings: 

Can Guppies Live Alone?

How many Goldfish In a 20-Gallon Tank?

How Many Guppies in a 20-Gallon Tank?

If you have a 20-gallon tank waiting to welcome guppies, you could accommodate ten guppies as per the thumb rule. The best male-female ratio could be 2 to 3 males, and 7 to 8 females would be perfect. However, if you are an experienced aquarist and know how to care for guppies the best, you can even keep up to 12 guppies in the aquarium. 

The size of Guppies can make you believe you could stock more than 10 to 12 Guppies in a 20 gallon (75 liters) tank, do not fall prey to this tendency; over-stocking causes numerous problems.

How to Add More Guppies to a 10-Gallon or 20-Gallon tank?

Are you someone who loves to have an overcrowded tank? I would not recommend it unless you have several years of experience to boast. A confined environment as such is not great for your Guppies; over-stocking is one of the primary causes of failure in aquarium keeping. 

However, if you are the one who is with a certain number of years of experience and can ensure all the essential measures and confidence to take proper care of all the fish in a 10–20-gallon tank, then you could dive in for it. 

Filtration and Bio Media

Most of the aquarium kits come with an internal filter. These filters are usually great for 10–20-gallon tanks. Though the guppies are not that messier, adding filtration will keep the tank water clean, which, in turn, will let them have good health. But internal filters not sufficient for overstocked aquariums.

To enhance the fish-holding capacity of your aquarium, opt for a canister filter or hang-on-back filter that has a better water flow rate. Also, adding an external filter can be beneficial as it holds a certain amount of water to increase the tank’s overall water volume.

Along with the filter, you also need to add a very fine filter media. For an overstocked tank, sponge media will not be sufficient. Thus, you can add a biological filter media. A bio-media with its vast surface area will house more beneficial bacteria (nitrification bacterias) to break down the maximal amount of toxic elements, ammonia, nitrites, and nitrates.


While overstocking a tank, you need to take special care of the substrate laid in it. Usually, gravel is the most anticipated one. But it takes up much space and does not aid your aquarium with the self-cleaning process.  

So, replace the gravel with other substrates that can house more nitrifying bacteria. If you are thinking of using gravel for your aquarium, make sure you vacuum clean every time you change the water. 

Live Aquarium Plants and Decors

Live plants are great for caring for guppies and giving them a suitable aquatic ambiance in their habitat. These live plants in an overstocked aquarium will enhance the oxygen level and offer your guppies to play and nurture their curiosity.

Also, live plants will improve tank water quality as it absorbs a considerable amount of nitrates and other toxins produced from fish wastes. Plants such as Water Wisteria, Amazon Sword, Guppy grass, Java ferns, Watersprite, Elodea, Java Moss, Anacharis, duckweed, giant duckweed, water lettuce, etc., are suitable for your Guppy tank; and also some red aquarium plants, such as Echinodorus Fancy Twists, Red Tiger Lotus, Rotala Rotundifolia, Rotala Indica, etc. are fitting for Guppy tanks.

If you know how to play with different plants in decorating the Guppy, you most probably won’t need any other decors; however, adding caves, tubes, rocks, etc., would give more room for their curiosity and make them more dynamic.

Water Parameters

For facilitating the best care to your guppies, you would want to ensure the water temperature is around 72-82℉. Guppies typically prefer neutral to slightly soft water; thus, the tank water pH needs to be about 6.8-7.8 and maintain the water hardness between 8-12 dGH. Lastly, ensure the nitrates level in the water does not exceed 10ppm at any given time.


Be Ready for Newborns/ Fry

Guppies are highly prolific species and reproduce in the right setting at an alarming rate. 

Guppies are livebearers, meaning they do not lay eggs; they reproduce free swimming babies. The adult Guppies devour their babies for a snack; despite some fry will survive taking shelter in the plants like Java moss where infusorian, the first fry food is in abundance and grow to become adults.

Hence, your tank population will eventually grow. Thus, to be prepared from the very beginning, pick a larger capacity tank to accommodate newborn guppies without overstocking the tank.

Troubles of Overstocking

trouble of overstocking

It’s not just enough to ask how many Guppies per gallon or how many Guppies in a 10-gallon tank or 20-gallon tank; overcrowding the habitat should be a concern for you when deciding to adopt guppies. Owing to their size, it is easy to overstock them by overlooking the guideline for housing Guppies in an aquarium tank.

Overstocking your guppy tank comes with potential risks. Overstocking affects the health and life of any pet fish. Thus, it is a significant concern for all tank owners. Here are some issues I’ve enlisted on the matter of overstocking guppies in your aquarium.

Too much Bio-load

Fish waste produces ammonia, a toxic substance. The nitrifying bacteria housed in the filtration system transform ammonia into less poisonous substance nitrate through the nitrification process. However, the filtration system has its limit; when there is excess waste, ammonia could burn your fish fins, bodies leading to white cloud diseases, skin rot diseases, etc., and possibly premature death of your Guppies.

Difficult to maintain the water parameters of the tank:

It is challenging to maintain the water parameters stable in an over-populated tank; particularly in a small water body, the parameters can go off quickly without much warning.

Depletion of Oxygen

Over-population in the aquarium leads to depletion of dissolved oxygen levels in the water—lack of oxygen in the water results in drowning of the fish quite often.

Increases Stress

Guppies are bubbly and vivacious species, swims dynamically in the current, need a decent space. An over-populated tank can shrink each Guppy’s space and preventing their movement; this can stress the Guppies.

Stress is no good for anyone; it weakens their immune system; the fish become highly susceptible to various diseases.


Guppies are peaceful and friendly fish; nevertheless, they can become aggressive in certain conditions, such as during the mating time when the male-female ratio is off-balance, and while establishing pecking order, and when there is a lack of space for their movement.

Impair the growth rate

As it is, Guppy is a tiny species. An over-populated habitat can further stifle their growth and development; they can impact their moods, which may shorten their lifespan.

Demand for a more frequent water change

An over-crowded tank demands a more frequent water change, cleaning routine, etc. 

All this extra work can exhaust you and prevent you from enjoying your hobby; definitely, a sick aquarium tank will take away all the enthusiasm from you and your Guppies.


How many Guppies per Gallon?-Wrap Up

Now, you know how to calculate the space for your Guppies, the question “how many Guppies per Gallon” may seem amusing! 

First, you could take it slowly; consider the available space, time, and budget in deciding the tank size and the number of specimens. 

If you already have a tank, then go ahead prepare the tank for your Guppies and then measure the water-holding capacity of your tank. Then decide on the number of Guppies; remember the sex ratio while purchasing if you are looking forward to having a peaceful aquarium.

Enjoy your journey, and you could also share with us your experience; it will help other readers and us!

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