How Big Do Guppies Get?

So you are thinking about getting some fish, aren’t you?

Guppies actually make great first-time fish. They are low maintenance, don’t require crazy specific water parameters, and are extra colorful.

So what’s the answer?

  • How big guppies get
  • Why guppies stop growing
  • How to breed guppies for max size
TL;DR shortened version

How Big Do Guppies Get?

Your average guppy will be about 1-1.5 inches/ 2.5-3.8 cm long

Extra large guppies who have been bred under ideal conditions can reach 2 inches/ 5 cm long.

Supersized guppies can be as big as 3 to 3.5 inches/ 7.6 to 8.9 cm long. But don’t worry- since you are reading a beginner’s guide to guppies- yours won’t get that big. 

Why Do Guppies Stop Growing

There are multiple reasons that might lead to guppies stalling out on growth.

Part of it has to do with the fact that they become sexually active around the two-month-old mark, which can consume some of the energy needed to grow.

But that reason aside, let’s look at a couple more reasons why your guppies may not be growing.


Overcrowded tanks may not have enough space for the fish to grow properly. 

A 10-gallon tank should have no more than 6-7 guppies. And remember, the bigger the guppies the more space they are going to need. 

Overcrowding will lead to stress and competition for resources, which will not only stop your babies from growing to their full potential but will also affect how long your guppies live.

Poor Water Quality

Poor water quality can have a significant impact on your fish.

High levels of ammonia, nitrite, and nitrate can stress the fish out and slow down their development. 

To prevent stagnant growth, a water change of between 20%-50% of the tank volume with conditioned, temp-matched water is necessary at least once a week.

Proper filtration should also be in place, ideally with a filter that has been seasoned for at least 5-6 weeks. 

If not- that’s ok. It just means you have to change water more frequently. 

Poor Nutrition

Guppy fish tank

Guppies require a balanced and nutritious diet to grow healthily. 

Commercially available pellet food does the job, but live food would be ideal. 

A couple of examples of live food are brine shrimp (a crowd favorite), daphnia, or micro worms. 

Guppies should be fed 2-3 times a day in amounts they can eat in a few minutes. If you are using lights (mostly because you have a planted tank) then make sure to feed your guppies when the lights are on. 

Feeding guppies a poor-quality diet or insufficient food can stunt their growth and lead to nutritional deficiencies.

Water Temperature

Guppies are tropical fish, and maintaining the right water temperature is crucial for their growth. 

Water that is too cold or too hot can slow down their metabolism and therefore slow down growth.

Guppies thrive in water temperatures of 78-82 F. 

They are also highly sensitive to sudden temperature changes. That means you shouldn’t change the water temp by more than 1 degree every 24 hours.

If the temperature in their tank was below 78 degrees as they were growing then that might be why they stopped growing.  


Some guppies may have genetic factors that affect their growth potential. You can’t really control this part.

The reason I bring it up is sometimes you’ll have the perfect growing conditions but your guppies will almost refuse to grow. 

Stress and Illness

Guppies are fish that almost loves stress.

And I say this because they can find so many things to stress them out. 

And the aforementioned stress can kill them, too.

Whether it’s the water temp changing too quickly, being the wrong temp, overcrowding, lack of hiding spaces- you name it, they’ll stress over it. 

Stress is an easy fix, though. 

As long as you keep the tank up to date with maintenance- you’ll be 98% clear. 

When Do Guppies Reach Peak Size?

Guppies typically reach their maximum size within six to twelve months after birth. 

How big guppies grow will depend on the factors we’ve mentioned above, including genetics, diet, water quality, and overall care. 

Generally, male guppies will be smaller than females, and their growth might slow down as they age. 

I hate to sound like a broken record, but optimal conditions and nutrition are the name of the game when it comes to growing them to their full potential.

How To Breed Guppies For Size

Now that you know what influences guppies development, let’s take these concepts and compile them into actionable steps for you to follow.

Select Healthy Breeding Stock

Choose adult guppies that exhibit desirable traits, including good size, shape, and coloration. 

If you can, examine how they behave in a tank environment. Are they swimming around? Are they active? 

Guppies with any visible deformities or health issues will not make good candidates for breeding.

guppy fry

Provide The Optimal Tank Conditions

Create a spacious and well-maintained breeding tank with stable water parameters, proper filtration. Your best bet is to season a filter by using it in an existing tank for about 5-6 weeks.

That will allow beneficial bacteria that breaks down ammonia to develop and make your lift easier.

Make sure you maintain the right water parameters for ammonia, nitrite, nitrate, pH and temperature.

This is what it should look like:

  • Water temp: 78-82. Don’t change the water temp by more than 1 degree every 24 hours. 
  • pH: between 7-8
  • Ammonia: 0
  • Nitrite: 0
  • Nitrate: Below 20 (plants will help keep it down)

Offer a Nutritious Diet

Feed the breeding guppies a balanced and high-quality diet that includes live or frozen foods like brine shrimp, daphnia, and high-protein guppy pellets or flakes.

The more live food they can get- the better. They love this stuff and it’s filled with protein- which is exactly what their diet calls for. 

You want to feed them regularly, if possible on the same schedule every day. Feed them between 2-3 times a day.

What Do Guppies Like In Their Tank

Include plenty of hiding spots in the breeding tank, such as plants or aquarium decorations.

Plants have their own benefits to guppies as they help oxygenate the tank and give them another source of food that’s available whenever they want it.

It also provides females with a safe place to hide when they are pregnant, and- you guessed it right – reduce stress.

How Separating Genders Affects How Big Your Guppies Grow

To control breeding and prevent overpopulation, keep males and females separate until you are ready to begin the breeding process.

A single female guppies can give birth to some 1500 fry in her life cycle, which in return wears her down and eventually leads to old age and death.

You want to select the best pairs with desirable size and genetic traits for mating. Pair larger males with larger females to increase the chances of producing larger offspring.

Observe Mating Behaviors

Once the guppies are paired, monitor their behavior for signs of mating.

Male guppies will display courtship behaviors where they peruse the female pretty persistently almost to the point of her exhaustion. 

Once she is ready to mate she’ll stop hiding and avoid contact. 

Once pregnant, your guppy will become a lot less active, will tend to hide more and will spend more time by herself. 

She will do that to conserve energy- so if you spot this behavior it is completely normal.

Why You Want To Separate Fry from Adults

Once the fry are born, remove them from the breeding tank and place them in a separate tank to prevent them from becoming prey for adult guppies. 

You can also use a breeders box- which is a box with mess walls that you place in your existing tank. It gives the fry a place to safely swim. 

Fry should be fed 4-6 times a day in a diverse diet that includes live food and vegetables. Pellet and fish food is ok too, as long as its crushed- their mouth is small and they can eat big pieces. 

Continue Selective Breeding

As the fry mature, observe their growth and development.

You’ll be able to tell their sex around 4 weeks old. Separate them at this point, as they will start breeding again at 8 weeks old.

Breeding requires a lot of energy from them- energy that could be used for growing.

Select the largest and healthiest fry to continue breeding and further improve the size and quality of your guppies.

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